CN1668768A

CN1668768A - Martensitic stainless steel seamless pipe and manufacturing method thereof

Info

Publication number: CN1668768A
Application number: CN 03816735
Authority: CN
Inventors: 木谷茂; 谷田睦
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 2002-07-15
Filing date: 2003-07-07
Publication date: 2005-09-14
Anticipated expiration: 2023-07-07
Also published as: WO2004007780A1; EP1521856B1; MXPA05000454A; CN100355914C; CN101070579A; CA2491834C; BR0312612A; CA2491834A1; EP1521856A1; JP4126979B2; JP2004043935A; AR040354A1; AU2003280989A1; CN100532617C; ZA200500365B

Abstract

本发明提供一种马氏体不锈钢无缝管以及制造该无缝钢管的方法，所述无缝管没有内表面缺陷并可抑制在冲击加工部分中的滞后断裂产生。一种马氏体不锈钢无缝管，其特征在于，由下面组成： C：0.15～0.22％，Si：0.1～1.0％，Mn：0.10～1.00％，Cr：12.00～14.00％，P：0.020％或以下，S：0.010％或以下，N：0.05％或以下，O(氧)：0.0060％或以下，选自0.005～0.200％的V、Nb和Ti和0.0005～0.0100％的B中的至少一种成合金元素，以及余量Fe和杂质，满足下面的不等式(1)、(2)、(4)和(5)或下面的不等式(1)、(3)、(4)和(5)：C^*+10N^*≤0.45，(1)；H1≤－0.003(C^*+10N^*)+0.0016，(2)；H2≤－0.0018(C^*+10N^*)+0.00096，(3)；Cr^*≤9.0，(4)；S≤0.088N^*+0.00056，(5)。The present invention provides a martensitic stainless steel seamless pipe free from inner surface defects and capable of suppressing generation of hysteresis fracture in impact-worked portions and a method of manufacturing the seamless pipe. A martensitic stainless steel seamless pipe, characterized in that it consists of the following: C: 0.15-0.22%, Si: 0.1-1.0%, Mn: 0.10-1.00%, Cr: 12.00-14.00%, P: 0.020% or less, S: 0.010% or less, N: 0.05% or less, O (oxygen): 0.0060% or less, at least one selected from 0.005 to 0.200% of V, Nb and Ti and 0.0005 to 0.0100% of B The alloying elements, as well as the balance of Fe and impurities, satisfy the following inequalities (1), (2), (4) and (5) or the following inequalities (1), (3), (4) and (5) : C ^* +10N ^* ≤0.45, (1); H1≤－0.003 (C ^* +10N ^* )+0.0016, (2); H2≤－0.0018 (C ^* +10N ^* )+0.00096, (3); Cr ^* ≤9.0, (4); S≤0.088N ^* +0.00056, (5).

Description

Martensitic stainless steel seamless pipe and manufacture method thereof

Technical field

The present invention relates to a kind of martensitic stainless steel seamless pipe as being used for the steel pipe of oil well, described seamless tube can guarantee can not to take place the crackle that produced by delayed fracture.The present invention also relates to a kind of method that is used to prepare without any the Martensite Stainless Steel pipe of defect in inner surface such as the generation of inner scar.

Background technology

As the Martensite Stainless Steel pipe of oil well conduit such as the carbon that API-13%Cr generally includes about 0.2% content, this conduit needs 80ksi (552MPa) or higher high-yield strength and hot workability.Because high C and Cr content, the stainless steel tube after rolling has very high hardness, thereby toughness reduces.Therefore, the traditional Martensite Stainless Steel pipe after rolling can have by carried out the crackle that delayed fracture produced of shock load or static load processing in " impacting the part of processing " before thermal treatment.Therefore, in transportation or storage process, must be limited in the drop that " support " interior plate is stamped height and/or entered steel pipe support.And, the essential idle time that shortened before hot rolling thermal treatment afterwards.

Above-mentioned restriction in transportation or storage process can cause various defectives, as big dump, because plate is stamped the restriction of height and/or pipe drop, the working efficiency that is caused by the handled that does not have the ballistic stainless steel tube of excessive loads reduces, and makes from hot rolling in order to finish thermal treatment in the work period that limits and reduces to heat treated limiting time arrangement.

Japanese patent unexamined application H8-120415 discloses a kind of Martensite Stainless Steel that limits N content that has.In this patent specification, only be described in the tough property improvement after the thermal treatment.Yet, the N content of stainless steel tube in impacting the processing part and the relation of delayed fracture after rolling had not both been described, the undesirable heat processibility that does not also have description to cause owing to the increase of N content suppresses the measure of the defect in inner surface as inner scar.Making a kind of is unpractical to suppressing inner scar without any the weldless steel tube of measure.

Japanese patent unexamined application H6-306551 discloses an invention, and wherein, the restriction hydrogen richness improves toughness in the heat effect zone with the Martensite Stainless Steel pipe that has low carbon content by welding.In addition, Japanese patent unexamined application H5-255734 has described one the Martensite Stainless Steel pipe with low carbon content has been carried out dehydrogenation to prevent the invention of delayed fracture.These inventions relate to the Martensite Stainless Steel with low carbon content.Yet, do not provide the description that is concerning between the hydrogen richness and delayed fracture in the processing part about impacting at the rolling back Martensite Stainless Steel pipe that contains about 0.2% so high C.

Summary of the invention

The present invention's first purpose provides the Martensite Stainless Steel steel pipe of a kind of C of containing about 0.2%, and described steel pipe is suppressed at the delayed fracture of the impact processing part before the rolling postheat treatment, and does not produce inner scar.

Second purpose of the present invention provides a kind of method that is used to make the Martensite Stainless Steel pipe that does not produce inner scar, and described steel pipe is suppressed at the delayed fracture of the impact processing part before the rolling postheat treatment.

The inventor is by except that stipulating aptly in steel the content of various elements, also limits the relation of C (carbon), H (hydrogen), N (nitrogen) and S (sulphur) content and reaches first purpose.

And the present invention reaches second purpose by the condition of regulation wroughtsteel pipe.

The invention is characterized in that following Martensite Stainless Steel (A) and following being used to make the method (B) of Martensite Stainless Steel.In this manual, " % " is meant " the quality % " about every kind of constituent content.In addition, " rolling back steel pipe " expression forms by hot rolling but also the steel pipe of not heat-treating.

(A) a kind of martensitic stainless steel seamless pipe, it is characterized in that, form by following: by quality %, C:0.15～0.22%, Si:0.1～1.0%, Mn:0.10～1.00%, Cr:12.00～14.00%, P:0.020% or following, S:0.010% or following, N:0.05% or following, O (oxygen): 0.0060% or below, Al:0～0.1%, Ni:0～0.5%, Cu:0～0.25%, Ca:0～0.0050% and be selected from following mentioned those at least one group at least a alloying element (if contain two or more these alloying elements, then be total up to 0.005～0.200 quality %), and surplus Fe and impurity:

First group: be respectively V, Nb and the Ti of 0.005～0.200 quality %,

Second group: the B of 0.0005～0.0100 quality %, and its feature also is inequality (1), (2), (4) and (5) or following inequality (1), (3), (4) and (5) below satisfying:

C ^*+10N ^*≤0.45，????????????????(1)

H1≤-0.003(C ^*+10N ^*)+0.0016，???(2)

H2≤-0.0018(C ^*+10N ^*)+0.00096，?(3)

Cr ^*≤9.0，??????????????????????(4)

S≤0.088N ^*+ 0.00056, (5) are C wherein ^*Be effective solute carbon content (quality %) that equation (6) limits, N ^*Be effective solute nitrogen content (quality %) of equation (7) qualification, and Cr ^*Cr equivalent for equation (8) qualification, the H1 of inequality (2) is the residual hydrogen amount (quality %) in the steel pipe of rolling back, and the H2 of inequality (3) is the residual hydrogen amount (quality %) in the steel pipe after the thermal treatment, and the symbol of element in each equation or the inequality is the content (quality %) of corresponding element:

C ^*＝C-[12{(Cr/52)×(6/23)}/10]，?????????????(6)

N ^*＝N-[14{(V/51)+(Nb/93)}/10]

-[14{(Ti/48)+(B/11)+(Al/27)}/2]，???????(7)

Cr ^*＝Cr+4Si-(22C+0.5Mn+1.5Ni+30N)?????(8)。

In addition, preferred such steel pipe, it has 0.18～0.21% C content, 0.20～0.35% Si content, 12.40～13.10% Cr content, 0.003% or following S content and 0.035% or following N content.

(B) a kind of method that is used to make martensitic stainless steel seamless pipe is characterized in that, under the condition of inequality (9), adopts inclination roll type roll piercing mill pierced billet stainless steel below satisfying.Described stainless steel seamless pipe is made up of following: by quality %, C:0.15～0.22%, Si:0.1～1.0%, Mn:0.10～1.00%, Cr:12.00～14.00%, P:0.020% or following, S:0.010% or following, N:0.05% or following, O (oxygen): 0.0060% or below, Al:0～0.1%, Ni:0～0.5%, Cu:0～0.25%, Ca:0～0.0050% and be selected from following mentioned those at least one group at least a alloying element (if contain two or more these alloying elements, then be total up to 0.005～0.200 quality %), and surplus Fe and impurity:

First group: be respectively V, Nb and the Ti of 0.005～0.200 quality %,

Second group: the B of 0.0005～0.0100 quality %,

And all inequality (1), (4) and (5) below also satisfying:

C ^*+10N ^*≤0.45，?????????????????????????????(1)

Cr ^*≤9.0，???????????????????????????????????(4)

S≤0.088N ^*+0.00056，????????????????????????(5)

Cr ^*＜0.00009(C.A.+F.A.) ³-0.0035(C.A.+F.A.) ²

+ 0.0567 (C.A.+F.A.)+8.0024 (9) are C wherein ^*Be effective solute carbon content (quality %) that equation (6) limits, N ^*Be effective solute nitrogen content (quality %) of equation (7) qualification, and Cr ^*Cr equivalent for equation (8) qualification, C.A. in inequality (9) (〉=0 °) and F.A. represent crossing angle (toe angle) and feed angle (feed angle) respectively, and the symbol of element in each equation or the inequality is the content (quality %) of corresponding element:

C ^*＝C-[12{(Cr/52)×(6/23))/10]，???????????(6)

N ^*＝N-[14{(V/51)+(Nb/93)}/10]

-[14{(Ti/48)+(B/11)+(Al/27)}/2]，????(7)

Cr ^*＝Cr+4Si-(22C+0.5Mn+1.5Ni+30N)??(8)。

In addition, preferred such stainless steel tube, wherein has 0.18～0.21% C content, 0.20～0.35% Si content, 12.40～13.10% Cr content, 0.003% or following S content and 0.035% or following N content, and the method that is preferred for making martensitic stainless steel seamless pipe comprises following step (10) and (11) after the pierced billet:

(10) 920 ℃ or higher temperature soaking processing seamless,

(11) carry out hot rolling.

The accompanying drawing summary

Fig. 1 illustrates crackle and two parameters that produced by delayed fracture: effective solute carbon content (C ^*) and effective solute nitrogen content (N ^*) between graph of a relation.

Fig. 2 is illustrated in the steel pipe of rolling back after the residual hydrogen amount (H1) and thermal treatment the graph of a relation between the residual hydrogen amount (H2) in the steel pipe.

Fig. 3 illustrates crackle and two parameters that produced by delayed fracture: " C ^*+ 10N ^*" and rolling back steel pipe in graph of a relation between the residual hydrogen amount (H1).

Fig. 4 shows crackle and two parameters that produced by delayed fracture: " C ^*+ 10N ^*" and thermal treatment after the graph of a relation between the residual hydrogen amount (H2) in the steel pipe.

Fig. 5 is at effective solute nitrogen content (N ^*) and the mutual relationship of sulphur content in the appearance figure of inside scar.

Fig. 6 is at " crossing angle (C.A.)+feed angle (F.A.) " and Cr equivalent (Cr ^*) mutual relationship in the inside scar and the appearance figure of external defect.

Implement best mode of the present invention

The inventor thinks that the hysteresis crackle that impacts the processing part in Martensite Stainless Steel depends on solute C (carbon), solute N (nitrogen) and solute H (hydrogen), and they all are interstitial elements.The following a lot of experiments and the following fact (a) all are identified to (d):

(a) the delayed fracture susceptibility in the impact processing part of rolling back steel pipe depends on the amount, the particularly amount of solute N of solute C and solute N.

(b) amount of solute C influences the physical strength after the thermal treatment strongly, and the influence of the amount of solute N is less.Yet for the impact processing part of rolling back steel pipe, N significantly reduces anti-delayed fracture.

(c) when when improving anti-delayed fracture for the impact processing part of rolling back steel pipe and reduce N content, austenitic structure becomes unstable at high temperature, in the process of making steel pipe owing to bad hot workability causes a large amount of inside scars.Therefore, must suppress scar.

(d) for addressing this problem, for the consumption in operation in the minimum material (work strain) amount, according to the content of austenite generting element and ferrite generting element, the perforation angle (crossing angle) and the feed angle of regulation roll piercing mill.Therefore, this process can prevent inner scar.

To explain in detail below according to various conditions of the present invention, as the chemical constitution and the manufacture method of steel pipe.

1. the chemical constitution of steel pipe

The chemical constitution of Martensite Stainless Steel pipe of the present invention is determined as follows:

C：

C and N can provide the solid solution hardening of rolling back steel pipe together.In order to suppress to impact the delayed fracture of processing part by solid solution hardening, C content should be 0.22% or below, and be preferably 0.21% or below.Yet such minimizing C content makes and be difficult to obtain the purpose physical strength after thermal treatment.And, after causing manufacturing steel pipe, the excessive minimizing of C content produces scar, and this is the cause owing to delta ferrite, because C is the austenite generting element.Therefore, C content should for 0.15% or more than, and effectively the content of solute C should satisfy above-mentioned inequality (1).Its reason is explained later on.Preferred C content be 0.18% or more than.

Si：

Si makes in the process at steel and adds as oxygen scavenger.Being lower than 0.1% content can not be higher than 1.0% and then cause low toughness deoxygenation generation effect.Therefore, content should be 0.1～1.0%.Preferred content is 0.75% or following to obtain high tenacity.Preferred content is 0.20～0.35%.

Mn：

Mn is for improving steel physical strength effective elements, and makes in the process at steel and to add as oxygen scavenger.In addition, it is by forming the fixedly S in the steel of MnS, and the hot workability of giving.Be lower than 0.10% content for not effect of hot workability, surpass 1.00% and then cause low toughness.Therefore, content should be 0.1～1.0%.Preferred Mn content be 0.7% or below.

Cr：

Cr is the fundamental element that is used to improve the erosion resistance of steel.Particularly, be higher than 12.00% content and can improve the erosion resistance of plaque, but also greatly improve at CO ₂Erosion resistance under the environment.On the other hand,, therefore be higher than 14.00% Cr content and be easy in pyroprocess, produce delta ferrite, cause hot workability to reduce because Cr is the ferrite generting element.And excessive Cr content causes high production cost.Therefore, content should be 12.00%～14.00%, more preferably 12.40%～13.10%.

P：

P is included in the impurity in the steel.Excessive P content causes the low toughness of product after the thermal treatment.The admissible upper limit of P content should be 0.020%.Preferred P content is minimized to few as much as possible.

S：

Because S is the impurity that reduces hot workability, so S content should minimize.S content allow to be limited to 0.010%.This S content should satisfy above-mentioned inequality (5).Preferred S content be 0.003% or below.

N：

N is an austenite stabilizer element of improving the hot workability of steel.Yet N causes the delayed fracture of the impact processing part of rolling back steel pipe.Therefore, the upper limit of N content should be 0.05%.By the reduction that reduces the hot workability that N content causes by other element compensation, so N content should minimize.Preferred N content be 0.035% or below.

O (oxygen):

If make at steel and not remove oxygen in the process fully, then crackle or the streak quantity at billet surface increases, and produces outside scar in hot-rolled steel.Therefore, O content should minimize to 0.0060% or below.

V, Ti, Nb and B:

These elements combine with N and form nitride.If N content reduces, the inclusion more than a kind of element that then is selected from these elements reduces the solubleness quantity of solute N.Yet excessive N content causes very high hardness by the nitride that forms after thermal treatment, and causes erosion resistance and flexible to reduce.Therefore, V, Ti or Nb content should be respectively 0.005～0.200%, and B content should be 0.0005～0.0100%.If comprise two or more these alloying elements, then the total content of these elements should be 0.005～0.20%.

Al, Ni, Cu and Ca

Can comprise these elements if desired.Be added in the steel indeliberately for this element of " 0 " numeric representation in the content of one of these elements.

Al：

Al can make in the process when removing oxygen passable at steel, and can effectively be suppressed at the outside scar in the steel pipe.Yet excessive Al content causes that the degree of cleaning of steel descend, and also cause the obstruction of the immersion nozzle in the continuous casting process.Therefore, preferred Al content is 0～0.1%.

Ni：

Ni is an austenite stabilizer element, and improves the hot workability of iron and steel.Yet excessive N i content causes that the crack performance of anti-the sulphide stress corrosion descends.Therefore, preferred Ni content is 0～0.5%.

Cu：

Cu effectively improves corrosion resistance nature, and is the austenite stabilizer element of improving the steel hot workability.Yet Cu has low melting point, and excessive Cu content causes that hot workability reduces.Therefore, preferred Cu content is 0～0.25%.

Ca：

Ca combines and prevents sulphur segregation in crystal boundary with S in the steel, and this can cause the reduction of hot workability.Yet excess amount of Ca content causes big streak.Therefore, preferred Ca content is 0～0.0050%.

2. about inequality (1)～(5)

At first, inequality (1) is described.In order to be suppressed at the crackle that impacts the processing part, must improve anti-delayed fracture.Interstitial element such as C and N have improved the physical strength of steel, but make the anti-delayed fracture variation of impacting the processing part.In the steel pipe of rolling back, there is the unrelieved stress that causes by sizing mill or stretch-reducing mill hot rolling, this can reduce anti-delayed fracture more.

The inventor has studied C and the N influence for the delayed fracture of the impact processing part of rolling back API-13%Cr steel pipe.In the delayed fracture test, shock load puts on steel pipe, and the condition of shock load will be described in " embodiment ".The result has wherein used effective solute carbon (C shown in Fig. 1 and table 1～4 ^*) and effective solute nitrogen (N ^*).Use C ^*And N ^*Reason be described below.

The number of C atom combines with the Cr atom and forms carbide.As the C of interstitial element content can C content obtains the carbide by deducting from total C content.Therefore, effective solute carbon content (C ^*) limit by equation (6).

Similarly, some N atoms combine with V, Nb, Ti, B and Al atom and form nitride.As intermittence element N content can N content obtains in the nitride by deducting from total N content.Therefore, effective solute nitrogen content (N ^*) limit by equation (7).In equation (7), for Nb and V nitride, coefficient is 1/10, and this is because of the lower cause of separating out temperature, and for Ti, B and Al nitride, coefficient is 1/2, and this is because the higher cause of separating out temperature.

C and N are the interstitial elements in the steel.If their content is identical, they are roughly the same for the influence of physical strength and hardness.Yet C content is limited within 0.18～0.21% in the 13%Cr martensitic stainless steel seamless pipe of stipulating in the API-L80 grade, and described steel pipe is used for oil well.On the contrary, if N content is only used " 0.1% or lower " restriction, N content has wide selectivity so.Usually, N content is 0.01～0.05%, and this is lower than 1/10th of C content.Therefore, by effective solute carbon content (C ^*) and effective solute nitrogen content (N of 10 times ^*) between relation, study the performance of steel.

As shown in fig. 1, at the delayed fracture (crackle) that impacts the processing part along with C ^*And N ^*Both content reduces and reduces.Above-mentioned inequality (1) is by adopting linear interpolation to determine to the result.

Intermittently element such as C and N influences work hardening, this since work as steel pipe impact add man-hour cold working caused.Particularly, N provides dislocation to fix (pining), to improve work hardening.By experimental result, the inventor finds as " C ^*+ 10N ^*" amount be restricted to 0.45 or when lower, significantly suppressed because work hardening and the delayed fracture that hydrogen is led.

The delayed fracture of impacting the processing part is to be subjected to hydrogen richness and subsclerotic the influence.Must reduce effective solute carbon content (C ^*) and effective solute nitrogen content (N ^*), and reduce hardness thus, produce to suppress crackle.When steel is by owing to handle to impact when cold working and work hardening, even the low hydrogen crackle that also produces of initial hardness.Therefore, the content of residual hydrogen should reduce in steel pipe, to prevent the hydrogen crackle.

Residual hydrogen amount in the steel pipe of rolling back is different with the residual hydrogen amount behind the thermal treatment steel pipe.In the 13%Cr steel, there is mutual relationship between the residual hydrogen amount in the steel pipe of rolling back and the residual hydrogen amount behind the thermal treatment steel pipe, this is fixed basically because of thermal treatment temp.Quenching temperature is 920～980 ℃, and tempering temperature is 650～750 ℃.

Fig. 2 shows the H1 (rolling back) in the 13%Cr steel pipe that uses among the embodiment below and the graph of a relation of the residual hydrogen amount between the H2 (after the thermal treatment).For example, on the point of zero symbol that is identified by " a ", the residual hydrogen amount (H1) of rolling back steel pipe is about 3ppm, and the residual hydrogen amount (H2) after the thermal treatment is about 2ppm.

Above-mentioned inequality (2) has limited " C ^*+ 10N ^*" and H1 between relation, and above-mentioned inequality (3) has limited " C ^*+ 10N ^*" and H2 between relation.As mentioned above, C ^*And N ^*Increasing amount cause that intensity increases and toughness reduces, then because the hydrogen in the impact processing part has increased the susceptibility of delayed fracture.As a result, in order to suppress delayed fracture, must consider C ^*And N ^*Content and total relation of residual hydrogen amount.

Fig. 3 shows the result who obtains by following: research C content is the delayed fracture sensitivity of impact processing part of the rolling back steel pipe of 0.19% 13%Cr Martensite Stainless Steel, and the result is plotted in " C ^*+ 10N ^*" and the mutual relationship of H1 on.Fig. 4 shows similar result of study and has drawn " C ^*+ 10N ^*" and thermal treatment after the mutual relationship of H2.These results obtain in the following embodiments.

From the diagram of Fig. 3 and Fig. 4, can recognize if all satisfy above-mentioned inequality (1) and following inequality (2) and (3), then no longer produce at the delayed fracture (crackle) that impacts the processing part, wherein H1 is the residual hydrogen amount in the steel pipe of rolling back, and H2 is the residual hydrogen amount after the thermal treatment:

H1≤-0.003(C ^*+10N ^*)+0.0016，??????(2)

H2≤-0.0018(C ^*+10N ^*)+0.00096，????(3)

On the other hand, following inequality (4) and (5) expression are called as the effective Cr of defect in inner surface of inner scar and the scope of S content for inhibition.Satisfy the delayed fracture in the impact processing part after above-mentioned inequality (2) and (3) can be suppressed at rolling back steel pipe and thermal treatment.But, in the manufacturing processed of steel pipe, still might produce inner scar.

The generation of inner scar adopts roll piercing mill circumferential shearing strain in the pierced billet process to cause.In steel billet, shear-stress causes what have a different deformation resistance that part ofly has a crackle, and this is because the separating out and inclusion of ferrite/austenite grain boundary, sulphur.These crackles are out of shape in rolling process and cause inner scar.

For being suppressed at the crackle in ferrite/austenite grain boundary, δ-ferritic content should minimize.δ-ferritic content depends on Cr equivalent (Cr ^*), Cr in fact ^*Increase cause ferritic increase.Cr ^*Can be by following equation (8) expression, described equation (8) expression forms ferritic element and forms the linear relationship of austenitic element:

Cr ^*＝Cr+4Si-(22C+0.5Mn+1.5Ni+30N)????(8)

As in the equation (8) as can be seen, N is to Cr ^*Made very big contribution.When N content reduces when improving the toughness of rolling back steel pipe, the Cr equivalent increases and ferrite content increases, and this causes inner scar.Because these situations, the inequality (4) below therefore satisfying suppresses ferrite and inner scar:

Cr ^*≤9.0????(4)

Sulphur is separated out part also becomes crack reason.Separate out in order to suppress this, therefore sulphur content need be minimized.For this reason, S content should for 0.010% or below, preferred S content be 0.003% or below.Make the inclusion in the steel in the process, big streak and S content for reducing at steel, preferred oxygen (O) content be 0.0060% or below.

When reducing N for satisfying inequality (1) ^*During with the inhibition crackle, the Cr of equation (8) expression ^*Increase.This causes the increase of the ferritic phase that causes hot workability decline.For the recovery heat processibility, S content should reduce.

Fig. 5 shows at X-coordinate N ^*In the relation of ordinate zou S content, be lower than for 2% (representing) or be not less than the appearance figure of the inside scar of 2% (by symbol * expression) with symbol zero.This figure causes being suppressed by following inequality (5) restriction S content the approval of inner scar.Do not consider that from there being the working efficiency of interrupting processing standard lines is judged to be 2% inside scar generation:

S≤0.088N ^*+0.00056，????(5)

3. about manufacture method

In making the method for weldless steel tube of the present invention, the steel that has above mentioned chemical constitution and satisfy inequality (1), (4) and (5) carries out pierced billet under the help of transverse rolling roll shape roll piercing mill under the condition that inequality (9) is limited.

In order to suppress inner scar in the pierced billet process, importantly consideration is rolled the hot workability of steel and selects suitable rolling condition.

Various factors all influences and produces inner scar.In these factors, the feed angle of the king roller in the roll piercing mill and crossing angle play requisite effect.Usually, increase feed angle and crossing angle and reduce additional shearing strain in the pierced billet process, even and steel have poor hot workability, also can be under the condition that does not crack rolled iron.

Yet feed angle and crossing angle can not always increase easily.For obtaining that these angles are increased, need to replace main motor, even need to replace milling train.If steel has suitable hot workability in the operation of rolling, can select less relatively feed angle and crossing angle.Consider from the economic angle of making, in the operation of rolling, suppress relation between the promptly additional shearing strain of index of inner scar, can cause the preparation condition and the pierced billet condition of steel design that may be best about the exponential sum of hot workability.

The inventor has studied and has studied feed angle and the crossing angle experimental data for the influence of additional shearing strain in the past, and has further studied Cr ^*Relation between " C.A. (crossing angle)+F.A. (feed angle) " sum.As a result, have on the basis of same degree contribution for additional shear-stress, found Cr at feed angle and crossing angle ^*The mutual relationship of determining between " C.A.+F.A. ".

Fig. 6 shows at X-coordinate " C.A.+F.A. " and ordinate zou Cr ^*Mutual relationship in, be lower than for 2% (representing) or be not less than 2% the inside scar of (using symbol ● expression) and the appearance figure of external defect with zero.This figure causes thinking that no matter inner scar and external defect are that the boundary line that was lower than for 2% (representing with zero) or is not less than 2% (using symbol ● expression) all can be represented by cubic curve.The condition of the inequality (9) below satisfying causes inner scar generation to be suppressed.

Cr ^*＜0.00009(C.A.+F.A.) ³-0.0035(C.A.+F.A.) ²

+0.0567(C.A.+F.A.)+8.0024???????????????(9)

The right of inequality (9) is determined by inserting the gained data, and is represented above-mentioned border.

Manufacture method of the present invention can be included in the rolling reheat process before of the precision work of using stretch reducer.In this case, preferably the equal thermal treatment in the reheat process remain on 920 ℃ or more than.In the reheat process, reduce equal thermal treatment temp and cause that rolling back steel reduces in the T direction toughness perpendicular to rolling direction, reason is the incomplete recrystallization of the plain weave (flat grain) that forms in the course of processing.In addition, the zone of enrichment C and N produces around the carbide of Nb and/or V, and this is because the incomplete sosoloid or the diffusion of carbide and/or nitride.So, producing sclerosis and fragility in this zone, this causes delayed fracture.Preferably the following of the equal thermal treatment temp in the reheat process is limited to 920 ℃, or more preferably 1000 ℃, and preferred all thermal treatment temps on be limited to about 1100 ℃.

Embodiment

By preparation external diameter in 43 kinds of steel with the chemical constitution shown in table 1 and the table 2 is that 60.3mm and thickness are the seamless tube of 4.83mm.Then, these steel pipes are descended and test.

(1) delayed fracture test

Length is that the sample that drops hammer of 250mm is prepared by rolling back steel pipe.The weight test component of 150kg weight and most advanced and sophisticated 90mm curvature highly drops on the sample from 0.2m, and sample is in shock load (294J) distortion down.After one week, detect each sample and whether crack.By naked eyes, and also carry out crack detection by ultrasonic tesint (UST).Gained the results are shown in table 3 and the table 4.

Fig. 1 shows the crackle and effective solute carbon content (C that is produced ^*) and effective solute nitrogen content (N ^*) between graph of a relation.As shown in this Fig, the border that straight line " a " expression cracks.Straight line " a " can be by " C ^*+ 10N ^*"=0.45 " expression.Therefore, there is not the condition of delayed fracture generation by " C ^*+ 10N ^*"≤0.45 " expression.

(2) mensuration of residual hydrogen amount (H1 and H2)

The residual hydrogen amount of rolling back steel pipe and identical steel pipe use the analytical procedure of stipulating in JIS Z2614 to measure in the residual hydrogen amount after the thermal treatment.In thermal treatment, sample is 950 ℃ of shrends, then 700 ℃ of shrends.Test result is listed in table 3 and the table 4.

Fig. 2 is the H1 of expression sample and the graph of a relation between the H2.Can determine to exist the linear relationship that to represent approx by " H2=0.6H1 ".

(3) delayed fracture and three parameter: C ^*, N ^*And the relation between the residual hydrogen amount

In table 3 and table 4, list for the data that whether produce delayed fracture, represent respectively that for the online Fig. 4 of steel pipe after rolling back online Fig. 3 of steel pipe and the thermal treatment X-coordinate is represented " C among the figure ^*+ 10N ^*", and ordinate zou is represented the residual hydrogen amount.The straight line that whether cracks the border is respectively by following equation (2)-1 and (3)-1 expression.Therefore, the condition that does not produce delayed fracture satisfies above-mentioned inequality (2) or (3).And, even satisfy inequality (2) and (3), as " C ^*+ 10N ^*" be higher than at 0.45 o'clock and also delayed fracture might take place.So, should satisfy top inequality (1).

H1＝-0.003(C ^*+10N ^*)+0.0016??????(2)-1

H2＝-0.0018(C ^*+10N ^*)+0.00096????(3)-1。

Table 1

Numbering	Chemical constitution (surplus: Fe and impurity, quality %)
	Chemical constitution (surplus: Fe and impurity, quality %)																??C	??Si	??Mn	??P	??S	??Cr	??Ni	??Cu	??V	??Al	??N	??Nb	??Ti	??B	??Ca	??O
	????1 ????2 ????3 ????4 ????5 ????6 ????7 ????8 ????9 ????10 ????11 ????12 ????13 ????14 ????15 ????16 ????17 ????18 ????19 ????20 ????21 ????22 ????23 ????24 ????25	??0.19 ??0.18 ??0.19 ??0.21 ??0.20 ??0.19 ??0.20 ??0.21 ??0.20 ??0.19 ??0.18 ??0.20 ??0.18 ??0.20 ??0.20 ??0.21 ??0.20 ??0.21 ??0.18 ??0.19 ??0.18 ??0.20 ??0.20 ??0.20 ??0.21	??0.27 ??0.29 ??0.28 ??0.29 ??0.31 ??0.28 ??0.24 ??0.27 ??0.30 ??0.26 ??0.27 ??0.29 ??0.31 ??0.30 ??0.28 ??0.23 ??0.27 ??0.29 ??0.25 ??0.27 ??0.28 ??0.28 ??0.27 ??0.22 ??0.25	??0.85 ??0.89 ??0.82 ??0.76 ??0.72 ??0.91 ??0.94 ??0.88 ??0.76 ??0.77 ??0.82 ??0.84 ??0.79 ??0.83 ??0.87 ??0.84 ??0.78 ??0.86 ??0.88 ??0.76 ??0.91 ??0.84 ??0.89 ??0.92 ??0.89	??0.014 ??0.015 ??0.018 ??0.017 ??0.016 ??0.019 ??0.014 ??0.018 ??0.017 ??0.014 ??0.017 ??0.018 ??0.013 ??0.016 ??0.018 ??0.017 ??0.018 ??0.017 ??0.016 ??0.016 ??0.018 ??0.014 ??0.018 ??0.014 ??0.017	??0.001 ??0.002 ??0.003 ??0.001 ??0.002 ??0.001 ??0.001 ??0.002 ??0.001 ??0.003 ??0.001 ??0.002 ??0.001 ??0.003 ??0.002 ??0.001 ??0.002 ??0.001 ??0.002 ??0.001 ??0.002 ??0.003 ??0.001 ??0.001 ??0.001	??12.80 ??12.70 ??12.90 ??12.60 ??12.60 ??12.80 ??12.90 ??13.10 ??12.80 ??13.00 ??12.80 ??12.40 ??12.70 ??12.80 ??12.80 ??12.50 ??12.80 ??12.90 ??12.60 ??12.80 ??12.70 ??12.90 ??12.60 ??12.70 ??13.00	??0.08 ??0.14 ??0.12 ??0.07 ??0.34 ??0.21 ??0.09 ??0.34 ??0.45 ??0.21 ??0.26 ??0.35 ??0.21 ??0.27 ??0.12 ??0.08 ??0.04 ??0.05 ??0.03 ??0.06 ??0.09 ??0.14 ??0.1?9 ??0.07 ??0.33	??0.04 ??0.02 ??0.06 ??0.02 ??0.11 ??0.14 ??0.15 ??0.12 ??0.05 ??0.03 ??0.02 ??0.01 ??0.06 ??0.13 ??0.21 ??0.16 ??0.22 ??0.14 ??0.06 ??0.05 ??0.02 ??0.03 ??0.12 ??0.14 ??0.13	??0.040 ??0.030 ??0.080 ??0.040 ??0.090 ??0.060 ??0.110 ??0.080 ??0.160 ??0.090 ??0.050 ??0.120 ??0.110 ??0.080 ??0.090 ??0.070 ??0.130 ??0.030 ??0.020 ??0.040 ??0.030 ??0.050 ??0.050 ??0.100 ??0.090	??0.0013 ??0.0022 ??0.0019 ??0.0008 ??0.0014 ??0.0230 ??0.0240 ??0.0120 ??0.0030 ??0.0150 ??0.0150 ??0.0090 ??0.0050 ??0.0020 ??0.0030 ??0.0090 ??0.0070 ??0.0110 ??0.0070 ??0.0180 ??0.0160 ??0.0150 ??0.0210 ??0.0220 ??0.0110	??0.035 ??0.034 ??0.028 ??0.028 ??0.022 ??0.033 ??0.021 ??0.021 ??0.027 ??0.030 ??0.028 ??0.039 ??0.041 ??0.037 ??0.039 ??0.037 ??0.039 ??0.041 ??0.044 ??0.044 ??0.045 ??0.043 ??0.032 ??0.033 ??0.021	??0.001 ??0.002 ??0.005 ??0.003 ??0.006 ??0.004 ??0.003 ??0.005 ??0.008 ??0.009 ??0.002 ??0.001 ??0.001 ??0.003 ??0.01 ??0.015 ??0.016 ??0.006 ??0.009 ??0.004 ??0.006 ??0.002 ??0.002 ??0.004 ??0.004	??0.003 ??0.002 ??0.004 ??0.001 ??0.003 ??0.002 ??0.001 ??0.001 ??0.004 ??0.003 ??0.004 ??0.003 ??0.002 ??0.001 ??0.004 ??0.003 ??0.002 ??0.006 ??0.005 ??0.002 ??0.001 ??0.002 ??0.001 ??0.002 ??0.002	??0.0002 ??0.0001 ??0.0003 ??0.0004 ??0.0002 ??0.0005 ??0.0006 ??0.0007 ??0.0002 ??0.0006 ??0.0003 ??0.0002 ??0.0003 ??0.0007 ??0.0002 ??0.0007 ??0.0004 ??0.0002 ??0.0001 ??0.0003 ??0.0002 ??0.0001 ??0.0004 ??0.0005 ??0.0005	??0.0002 ??0.0003 ??0.0005 ??0.0006 ??0.0008 ??0.0021 ??0.0017 ??0.0018 ??0.0034 ??0.0032 ??0.0016 ??0.0018 ??0.0016 ??0.0018 ??0.0015 ??0.0019 ??0.0006 ??0.0008 ??0.0017 ??0.0024 ??0.0039 ??0.0048 ??0.0025 ??0.0019 ??0.0020	??C	??Si	??Mn	??P	??S	??Cr	??Ni	??Cu	??V	??Al	??N	??Nb	??Ti	??B	??Ca	??O	??0.0020 ??0.0030 ??0.0050 ??0.0040 ??0.0020 ??0.0010 ??0.0030 ??0.0040 ??0.0030 ??0.0050 ??0.0030 ??0.0030 ??0.0030 ??0.0050 ??0.0020 ??0.0010 ??0.0040 ??0.0030 ??0.0030 ??0.0020 ??0.0020 ??0.0020 ??0.0020 ??0.0030 ??0.0050

Table 2

Numbering	Chemical constitution (surplus: Fe and impurity, quality %)
	Chemical constitution (surplus: Fe and impurity, quality %)																??C	??Si	??Mn	??P	??S	??Cr	??Ni	??Cu	??V	??Al	??N	??Nb	??Ti	??B	??Ca	??O
	????26 ????27 ????28 ????29 ????30 ????31 ????32 ????33 ????34 ????35 ????36 ????37 ????38 ????39 ????40 ????41 ????42 ????43	??0.20 ??0.20 ??0.20 ??0.21 ??0.20 ??0.18 ??0.18 ??0.20 ??0.16 ??0.18 ??0.19 ??0.21 ??0.21 ??0.19 ??0.18 ??0.18 ??0.18 ??0.17	??0.28 ??0.25 ??0.27 ??0.27 ??0.25 ??0.24 ??0.28 ??0.26 ??0.21 ??0.27 ??0.29 ??0.31 ??0.27 ??0.22 ??0.25 ??0.26 ??0.26 ??0.26	??0.79 ??0.75 ??0.87 ??0.88 ??0.86 ??0.78 ??0.92 ??0.85 ??0.52 ??0.38 ??0.78 ??0.85 ??0.88 ??0.86 ??0.77 ??0.74 ??0.73 ??0.44	??0.015 ??0.012 ??0.017 ??0.016 ??0.015 ??0.016 ??0.017 ??0.013 ??0.014 ??0.017 ??0.018 ??0.022 ??0.013 ??0.013 ??0.014 ??0.012 ??0.011 ??0.012	??0.002 ??0.001 ??0.002 ??0.001 ??0.002 ??0.002 ??0.002 ??0.001 ??0.001 ??0.002 ??0.004 ??0.006 ??0.003 ??0.001 ??0.001 ??0.001 ??0.001 ??0.001	??12.90 ??12.90 ??12.60 ??12.80 ??12.50 ??12.60 ??12.50 ??12.80 ??13.10 ??12.90 ??12.80 ??12.70 ??13.00 ??12.90 ??12.70 ??12.90 ??13.10 ??13.20	??0.42 ??0.20 ??0.23 ??0.07 ??0.04 ??0.05 ??0.07 ??0.12 ??0.04 ??0.05 ??0.18 ??0.06 ??0.14 ??0.08 ??0.14 ??0.19 ??0.12 ??0.11	??0.04 ??0.05 ??0.04 ??0.12 ??0.07 ??0.04 ??0.05 ??0.04 ??0.04 ??0.03 ??0.05 ??0.04 ??0.03 ??0.13 ??0.02 ??0.02 ??0.02 ??0.06	??0.150 ??0.080 ??0.040 ??0.020 ??0.040 ??0.050 ??0.040 ??0.060 ??0.080 ??0.040 ??0.020 ??0.030 ??0.080 ??0.140 ??0.070 ??0.110 ??0.090 ??0.070	??0.0040 ??0.0140 ??0.0120 ??0.0130 ??0.0080 ??0.0150 ??0.0180 ??0.0170 ??0.0018 ??0.0150 ??0.0130 ??0.0030 ??0.0120 ??0.0140 ??0.0220 ??0.0200 ??0.0290 ??0.0022	??0.026 ??0.029 ??0.027 ??0.038 ??0.043 ??0.045 ??0.047 ??0.042 ??0.029 ??0.020 ??0.031 ??0.041 ??0.032 ??0.031 ??0.025 ??0.027 ??0.028 ??0.020	??0.007 ??0.006 ??0.004 ??0.003 ??0.007 ??0.003 ??0.005 ??0.003 ??0.002 ??0.004 ??0.007 ??0.005 ??0.004 ??0.003 ??0.003 ??0.002 ??0.003 ??0.004	??0.003 ??0.003 ??0.004 ??0.005 ??0.006 ??0.003 ??0.002 ??0.004 ??0.003 ??0.004 ??0.007 ??0.002 ??0.001 ??0.002 ??0.005 ??0.003 ??0.005 ??0.002	??0.0003 ??0.0007 ??0.0004 ??0.0005 ??0.0002 ??0.0002 ??0.0001 ??0.0003 ??0.0003 ??0.0005 ??0.0007 ??0.0002 ??0.0004 ??0.0002 ??0.0002 ??0.0002 ??0.0004 ??0.0003	??0.0032 ??0.0028 ??0.0014 ??0.0004 ??0.0013 ??0.0025 ??0.0031 ??0.0022 ??0.0011 ??0.0008 ??0.0021 ??0.0018 ??0.0009 ??0.0012 ??0.0019 ??0.0024 ??0.0029 ??0.0028	??C	??Si	??Mn	??P	??S	??Cr	??Ni	??Cu	??V	??Al	??N	??Nb	??Ti	??B	??Ca	??O	??0.0020 ??0.0030 ??0.0010 ??0.0050 ??0.0030 ??0.0020 ??0.0010 ??0.0040 ??0.0030 ??0.0040 ??0.0050 ??0.0020 ??0.0080 ??0.0020 ??0.0020 ??0.0020 ??0.0030 ??0.0040

Table 3

Numbering	?C ^*	??N ^*	??C ^+ ??10N ^	? ①	Rolling back residual hydrogen (H1)	? ??②	? ③	Residual hydrogen after the thermal treatment (H2)	? ??④	? ⑤	Delayed fracture	????Cr ^*	? ?⑥	? ??⑦	? ?⑧	Inner scar	Outside scar	Estimate
Numbering	?C ^*	??N ^*	??C ^+ ??10N ^	? ①	Rolling back residual hydrogen (H1)	? ??②	? ③	Residual hydrogen after the thermal treatment (H2)	? ??④	? ⑤	Delayed fracture	????Cr ^*	? ?⑥	? ??⑦	? ?⑧	Inner scar	Outside scar	Estimate	????1 ????2 ????3 ????4 ????5 ????6 ????7 ????8 ????9 ????10 ????11 ????12 ????13 ????14 ????15 ????16 ????17 ????18 ????19 ????20 ????21 ????22 ????23 ????24 ????25	?0.113 ?0.104 ?0.112 ?0.134 ?0.124 ?0.113 ?0.122 ?0.131 ?0.123 ?0.112 ?0.103 ?0.125 ?0.104 ?0.123 ?0.123 ?0.135 ?0.123 ?0.132 ?0.104 ?0.113 ?0.104 ?0.122 ?0.124 ?0.124 ?0.132	??0.0330 ??0.0322 ??0.0245 ??0.0262 ??0.0185 ??0.0247 ??0.0112 ??0.0150 ??0.0210 ??0.0227 ??0.0219 ??0.0328 ??0.0362 ??0.0336 ??0.0349 ??0.0316 ??0.0328 ??0.0362 ??0.0407 ??0.0377 ??0.0397 ??0.0374 ??0.0248 ??0.0239 ??0.0150	??0.443 ??0.426 ??0.357 ??0.397 ??0.309 ??0.360 ??0.234 ??0.281 ??0.333 ??0.339 ??0.322 ??0.453 ??0.465 ??0.459 ??0.472 ??0.451 ??0.451 ??0.495 ??0.511 ??0.490 ??0.500 ??0.496 ??0.372 ??0.362 ??0.282	○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × × × × × × × × × × × ○ ○ ○	??0.00005 ??0.00007 ??0.00005 ??0.00005 ??0.00025 ??0.00027 ??0.00030 ??0.00020 ??0.00010 ??0.00020 ??0.00020 ??0.00022 ??0.00005 ??0.00021 ??0.00017 ??0.00019 ??0.00024 ??0.00011 ??0.00005 ??0.00011 ??0.00008 ??0.00009 ??0.00044 ??0.00060 ??0.00072	??0.00027 ??0.00032 ??0.00053 ??0.00041 ??0.00067 ??0.00052 ??0.00090 ??0.00076 ??0.00060 ??0.00058 ??0.00063 ??0.00024 ??0.00020 ??0.00022 ??0.00018 ??0.00025 ??0.00025 ??0.00012 ??0.00007 ??0.00013 ??0.00010 ??0.00011 ??0.00048 ??0.00051 ??0.00075	○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × ○	??0.000030 ??0.000040 ??0.000040 ??0.000030 ??0.000140 ??0.000160 ??0.000190 ??0.000110 ??0.000040 ??0.000090 ??0.000130 ??0.000120 ??0.000040 ??0.000100 ??0.000090 ??0.000080 ??0.000130 ??0.000068 ??0.000037 ??0.000077 ??0.000050 ??0.000040 ??0.000270 ??0.000380 ??0.000430	??0.000163 ??0.000194 ??0.000317 ??0.000246 ??0.000403 ??0.000312 ??0.000538 ??0.000453 ??0.000361 ??0.000351 ??0.000380 ??0.000144 ??0.000122 ??0.000133 ??0.000111 ??0.000148 ??0.000148 ??0.000070 ??0.000040 ??0.000078 ??0.000060 ??0.000067 ??0.000291 ??0.000308 ??0.000453	○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × ○	○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?× ?× ?× ?× ?× ?× ?× ?× ?× ?× ?× ?○ ?× ?○	????8.105 ????8.225 ????8.410 ????7.815 ????7.910 ????7.980 ????8.225 ????7.980 ????7.735 ????8.260 ????8.280 ????7.045 ????8.040 ????7.670 ????7.735 ????7.150 ????7.860 ????7.705 ????7.835 ????7.910 ????7.920 ????7.700 ????7.590 ????7.625 ????7.810	○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○	??0.003463 ??0.003395 ??0.002713 ??0.002870 ??0.002189 ??0.002735 ??0.001544 ??0.001882 ??0.002408 ??0.002556 ??0.002490 ??0.003446 ??0.003744 ??0.003521 ??0.003630 ??0.003344 ??0.003449 ??0.003748 ??0.004142 ??0.003877 ??0.004051 ??0.003847 ??0.002738 ??0.002662 ??0.001881	○ ?○ ?× ?○ ?○ ?○ ?○ ?× ?○ ?× ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○	?○ ??○ ??× ??○ ??○ ??○ ??○ ??× ??○ ??× ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○	??○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○ ????○	?○ ??○ ??× ??○ ??○ ??○ ??○ ??× ??○ ??× ??○ ??× ??× ??× ??× ??× ??× ??× ??× ??× ??× ??× ??○ ??× ??○
Numbering 1,2,4-7,9,11,23 and 25: the present invention numbers 3,8,10,12-22 and 24: contrast 1.: inequality (1) is satisfied (zero) or do not satisfy () not 2.: the calculated value on inequality (2) the right 3.: inequality (2) is satisfied (zero) or do not satisfy () not 4.: the calculated value on inequality (3) the right 5.: inequality (3) is satisfied (zero) or do not satisfy () not 6.: inequality (4) is satisfied (zero) or do not satisfy () not 7.: the calculated value on inequality (5) the right 8.: inequality (5) is satisfied (zero) or do not satisfy (*)																							○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × × × × × × × × × × × ○ ○ ○			○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × ○			○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × ○

Table 4

Numbering	?C ^*	??N ^*	??C ^+ ??10N ^	? ?①	Rolling back residual hydrogen (H1)	? ??②	? ③	Residual hydrogen after the thermal treatment (H2)	? ??④	? ??⑤	Delayed fracture	???Cr ^*	? ?⑥	? ??⑦	? ?⑧	Outside scar	Inner scar	Estimate
Numbering	?C ^*	??N ^*	??C ^+ ??10N ^	? ?①	Rolling back residual hydrogen (H1)	? ??②	? ③	Residual hydrogen after the thermal treatment (H2)	? ??④	? ??⑤	Delayed fracture	???Cr ^*	? ?⑥	? ??⑦	? ?⑧	Outside scar	Inner scar	Estimate	????26 ????27 ????28 ????29 ????30 ????31 ????32 ????33 ????34 ????35 ????36 ????37 ????38 ????39 ????40 ????41 ????42 ????43	?0.122 ?0.122 ?0.124 ?0.133 ?0.125 ?0.104 ?0.105 ?0.123 ?0.081 ?0.102 ?0.113 ?0.134 ?0.132 ?0.112 ?0.104 ?0.102 ?0.101 ?0.091	??0.0201 ??0.0222 ??0.0219 ??0.0330 ??0.0387 ??0.0391 ??0.0408 ??0.0351 ??0.0257 ??0.0141 ??0.0255 ??0.0389 ??0.0262 ??0.0231 ??0.0165 ??0.0182 ??0.0170 ??0.0170	??0.323 ??0.344 ??0.343 ??0.463 ??0.512 ??0.495 ??0.513 ??0.474 ??0.338 ??0.243 ??0.368 ??0.523 ??0.394 ??0.343 ??0.268 ??0.284 ??0.271 ??0.260	○ ?○ ?○ ?× ?× ?× ?× ?× ?○ ?○ ?○ ?× ?○ ?○ ?○ ?○ ?○ ?○	??0.00070 ??0.00060 ??0.00065 ??0.00020 ??0.00005 ??0.00005 ??0.00005 ??0.00010 ??0.00005 ??0.00011 ??0.00008 ??0.00024 ??0.00012 ??0.00004 ??0.00008 ??0.00019 ??0.00013 ??0.00004	??0.00063 ??0.00057 ??0.00057 ??0.00021 ??0.00006 ??0.00011 ??0.00006 ??0.00018 ??0.00059 ??0.00087 ??0.00050 ??0.00003 ??0.00042 ??0.00057 ??0.00080 ??0.00075 ??0.00079 ??0.00082	× × × ○ ○ ○ ○ ○ ○ ○ ○ × ○ ○ ○ ○ ○ ○	??0.000410 ??0.000350 ??0.000410 ??0.000100 ??0.000020 ??0.000030 ??0.000036 ??0.000060 ??0.000010 ??0.000070 ??0.000040 ??0.000150 ??0.000060 ??0.000010 ??0.000040 ??0.000110 ??0.000070 ??0.000010	??0.000378 ??0.000340 ??0.000342 ??0.000127 ??0.000038 ??0.000068 ??0.000037 ??0.000106 ??0.000352 ??0.000523 ??0.000298 ??0.000019 ??0.000251 ??0.000343 ??0.000477 ??0.000448 ??0.000472 ??0.000492	?× ??× ??× ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??× ??○ ??○ ??○ ??○ ??○ ??○	??× ????× ????× ????× ????× ????× ????× ????× ????○ ????○ ????○ ????× ????○ ????○ ????○ ????○ ????○ ????○	???7.815 ???7.955 ???7.690 ???7.575 ???7.320 ???7.785 ???7.685 ???7.575 ???9.230 ???9.155 ???8.190 ???7.575 ???7.850 ???8.120 ???8.395 ???8.515 ???8.795 ???9.515	○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?× ?× ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?×	??0.002330 ??0.002514 ??0.002487 ??0.003463 ??0.003967 ??0.004003 ??0.004151 ??0.003651 ??0.002820 ??0.001797 ??0.002805 ??0.003984 ??0.002868 ??0.002590 ??0.002010 ??0.002162 ??0.002054 ??0.002053	○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?× ?× ?× ?× ?○ ?○ ?○ ?○ ?○	?○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??× ??× ??× ??× ??× ??○ ??○ ??○ ??○ ??×	?○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??○ ??× ??○ ??○ ??○ ??○ ??○	??× ????× ????× ????× ????× ????× ????× ????× ????× ????× ????× ????× ????× ????○ ????○ ????○ ????○ ????×
Numbering 39-42: the present invention numbers 26-38 and 43: contrast 1.: inequality (1) is satisfied (zero) or do not satisfy () not 2.: the calculated value on inequality (2) the right 3.: inequality (2) is satisfied (zero) or do not satisfy () not 4.: the calculated value on inequality (3) the right 5.: inequality (3) is that 6. satisfied (zero) or () does not satisfy: inequality (4) is that 7. satisfied (zero) or () does not satisfy: the calculated value on inequality (5) the right 8.: inequality (5) is that satisfied (zero) or (*) does not satisfy																							○ ?○ ?○ ?× ?× ?× ?× ?× ?○ ?○ ?○ ?× ?○ ?○ ?○ ?○ ?○ ?○			× × × ○ ○ ○ ○ ○ ○ ○ ○ × ○ ○ ○ ○ ○ ○						○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?× ?× ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?×		○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?○ ?× ?× ?× ?× ?○ ?○ ?○ ?○ ?○

(4) inner scar detects

By being chosen in several steel of the content in table 1 and 2, under the condition of " C.A.+F.A. "=9, prepare 500 steel pipes, and detect inner scar and whether produce with various effective solute N and sulphur.The result is shown in Figure 5.The line that inclines is represented that inner scar produces and is lower than or is higher than 2% border.It can pass through equation (5)-1 expression.Therefore, inner scar can be suppressed by the inequality (5) above satisfying.

S＝0.088N ^*+0.00056??(5)-1

By several steel in option table 1 and 2, prepare 50 steel pipes from steel billet under the condition below, it has different Cr equivalent (Cr listed in table 5 ^*), detect then and determine whether to produce inner scar:

(1) Heating temperature of steel billet: 1200～1250 ℃

(2) decrement of the steel billet diameter of plug tip: 5.0～8.0%

(3) C.A.+F.A.:10,17,21 and 30

Table 5 shows inner scar and produces and two parameter: Cr ^*Relation between " C.A.+F.A. ".In table 5 and Fig. 6, inner scar of zero symbolic representation and outside scar all are lower than 2%, and symbol ● represent that inner scar and outside scar all are higher than 2%.

Fig. 6 is an operation parameter in table 5: " C.A.+F.A. " and Cr ^*Line chart as a result.Cubic curve among this figure is represented by following equation (9)-1.Therefore, suppressing the condition that inner scar produces is to satisfy above-mentioned inequality (9).

Cr ^*＝0.00009(C.A.+F.A.) ³-0.0035(C.A.+F.A.) ²

+0.0567(C.A.+F.A.)+8.0024????????????(9)-1

Table 5

Numbering	??Cr ^*	????????????????????????????????????????????????????????????C.A.+F.A.
						????10	????17	????21	????30
		????9	??7.735	????○	????○	????10	????17	????21	????30	????○	????○
????4	??7.815	????9	??7.735	????○	????○	????○	????○	????○	????○	????○	????○
????4	??7.815	????6	??7.980	????○	????○	????○	????○	????○	????○	????○
????39	??8.120	????6	??7.980	????○	????○	????○	????○	????○	????○	????○
????39	??8.120	????7	??8.225	????○		????○	????○	????○	????○
????11	??8.280	????7	??8.225	????○		????○	????○	????○
????11	??8.280	????40	??8.395	????●		????○	????○	????○		????○
????41	??8.515	????40	??8.395	????●		????●	????●	????●	????○	????○
????41	??8.515	????42	??8.795	????●	????●	????●	????●	????●	????○	????●	????○
????35	??9.155	????42	??8.795	????●	????●		????●	????●	????○	????●	????○
????35	??9.155	????34	??9.230				????●	????●	????○	????●	????●
????43	??9.515	????34	??9.230						????●	????●	????●

Industrial usability

When impacting cold working in the processing procedure after 13%Cr martensite seamless steel pipe of the present invention is manufacturing pipe, it can prevent delayed fracture. This steel pipe has excellent corrosion resistance, and is particularly useful for oil well. Manufacturing method according to the invention can produce the 13%Cr martensite seamless steel pipe that does not have inner scar to produce.

Claims

1. A martensitic stainless steel seamless pipe, characterized in that it consists of the following: by mass %, C: 0.15-0.22%, Si: 0.1-1.0%, Mn: 0.10-1.00%, Cr: 12.00- 14.00%, P: 0.020% or less, S: 0.010% or less, N: 0.05% or less, O (oxygen): 0.0060% or less, Al: 0-0.1%, Ni: 0-0.5%, Cu: 0 to 0.25%, Ca: 0 to 0.0050% and at least one element selected from at least one group mentioned below (if two or more of these elements are contained, 0.005 to 0.200% by mass in total), and Balance Fe and impurities:

The first group: 0.005-0.200% by mass of V, Nb and Ti, respectively,

The second group: 0.0005-0.0100% by mass of B,

And it is also characterized in that the following inequalities (1), (2), (4) and (5) or the following inequalities (1), (3), (4) and (5) are satisfied:

C ^* +10N ^* ≤0.45, (1)

H1≤-0.003(C ^* +10N ^* )+0.0016, (2)

H2≤-0.0018(C ^* +10N ^* )+0.00096, (3)

Cr ^* ≤9.0, (4)

S≤0.088N ^* +0.00056, (5)

where C ^* is the effective solute carbon content (mass %) defined by the following equation (6), N ^* is the effective solute nitrogen content (mass %) defined by the equation (7), and Cr ^* is the effective solute nitrogen content (mass %) defined by the equation (8) Cr equivalent, H1 of inequality (2) is the residual hydrogen (mass %) in the steel pipe after rolling, and H2 of inequality (3) is the residual hydrogen (mass %) in the steel pipe after heat treatment, and each The element symbol in the equation or inequality is the content (mass%) of the corresponding element:

C ^* ＝C-[12{(Cr/52)×(6/23)}/10], (6)

N ^* ＝N-[14{(V/51)+(Nb/93)}/10]

-[14{(Ti/48)+(B/11)+(Al/27)}/2], (7)

Cr ^* = Cr+4Si-(22C+0.5Mn+1.5Ni+30N) (8).

2. The martensitic stainless steel seamless pipe according to claim 1, wherein the C content is 0.18 to 0.21% by mass, the Si content is 0.20 to 0.35% by mass, the Cr content is 12.40 to 13.10% by mass, and the S content is 0.003% by mass % or less and the N content is 0.035% by mass or less.

3. A method for manufacturing a martensitic stainless steel seamless pipe, characterized in that the stainless steel is pierced and rolled using an inclined roll type piercing and rolling mill under the condition that the following inequality (9) is satisfied. The stainless steel seamless pipe is composed of the following: by mass %, C: 0.15-0.22%, Si: 0.1-1.0%, Mn: 0.10-1.00%, Cr: 12.00-14.00%, P: 0.020% or less, S: 0.010% or less, N: 0.05% or less, O (oxygen): 0.0060% or less, Al: 0-0.1%, Ni: 0-0.5%, Cu: 0-0.25%, Ca: 0-0.0050 % and at least one alloying element selected from at least one group mentioned below (if two or more of these alloying elements are contained, the total is 0.005 to 0.200% by mass), and the balance Fe and impurities:

The first group: 0.005-0.200% by mass of V, Nb and Ti, respectively,

The second group: 0.0005-0.0100% by mass of B,

And it also satisfies all of the following inequalities (1), (4) and (5):

C ^* +10N ^* ≤0.45, (1)

Cr ^* ≤9.0, (4)

S≤0.088N ^* +0.00056, (5)

Cr ^* ＜0.00009(CA+FA) ³ -0.0035(CA+FA) ²

+0.0567(C.A.+F.A.)+8.0024 (9)

where C ^* is the effective solute carbon content (mass %) defined by the following equation (6), N ^* is the effective solute nitrogen content (mass %) defined by the equation (7), and Cr ^* is the effective solute nitrogen content (mass %) defined by the equation (8) Cr equivalent, CA (≥0°) and FA in inequality (9) represent crossing angle and feeding angle respectively, and the element symbol in each equation or inequality is the content (mass %) of corresponding element:

C ^* ＝C-[12{(Cr/52)×(6/23)}/10], (6)

N ^* ＝N-[14{(V/51)+(Nb/93)}/10]

-[14{(Ti/48)+(B/11)+(Al/27)}/2], (7)

Cr ^* = Cr+4Si-(22C+0.5Mn+1.5Ni+30N) (8).

4. The method for manufacturing a martensitic stainless steel seamless pipe as claimed in claim 3, wherein the C content is 0.18 to 0.21 mass%, the Si content is 0.20 to 0.35 mass%, and the Cr content is 12.40 to 13.10 mass%, The S content is 0.003% by mass or less and the N content is 0.035% by mass or less.

5. The method for manufacturing martensitic stainless steel seamless pipe as claimed in claim 3 or 4, characterized in that, the method also comprises the following steps (10) and (11) after piercing and rolling:

(10) soaking seamless pipes at a temperature of 920°C or higher,

(11) Perform hot rolling.