JP2009532584A - Low carbon alloy steel pipe with ultra-high strength and excellent toughness at low temperature and its production method - Google Patents

Abstract

  The steel tube is essentially about 0.06% to about 0.18% carbon, about 0.3% to about 1.5% manganese, about 0.05% to about 0.5% by weight. Silicon, up to about 0.015% sulfur, up to about 0.025% phosphorus and at least one of the following elements: up to about 0.30% vanadium, up to about 0.10% aluminum, about .0. Up to 06% niobium, up to about 1% chromium, up to about 0.70% nickel, up to about 0.70% molybdenum, up to about 0.35% copper, up to about 0.15% residual elements and residue A low-carbon alloy steel pipe, particularly for a pressure vessel of an air pump for a storage gas, and a method for producing the same. After a high heating rate of about 100 ° C. per second, the steel tube is rapidly and completely quenched in a water base quench solution at a cooling rate of about 100 ° C. per second. Steel has a high tensile strength of at least about 145 ksi and 220 ksi and exhibits ductile behavior at low temperatures such as -100 ° C.

Description

Cross-reference of related applications

  This PCT application claims priority from US Patent Application No. 11 / 395,322, filed April 3, 2006.

  The present invention is directed to a low carbon alloy steel pipe having ultra-high strength and excellent toughness at low temperatures and a method for producing such a steel pipe. Steel pipes are particularly suitable for producing components for the containment of automobile restraint systems, one example of which is an air pump for an automobile airbag.

  In addition, alternative steel compositions in low carbon, low alloy categories and different heat treatment methods were developed and tested to reduce manufacturing costs.

  Patent Literature 1 and Patent Literature 2 describe, in general terms, steel chemistry that is considered useful for an air pump of an automobile airbag (see Patent Literatures 1 and 2). These references cite the absence of heat treatment, stress relief and annealing or quenching and tempering as final conditions. These publications do not mention the possibility of quenching alone as a heat treatment step. The claims do not mention mechanical properties. In various examples, the steel was quenched and tempered only in Example # 21, but the only reported UTS is 686 MPa (99 ksi). Even the best described mechanical properties in Example # 26 are relatively low, with a maximum UTS of 863 MPa (125 ksi). Therefore, these publications target a relatively low grade (the intended target is 590 MPa (86 ksi)). In addition, these publications exhibit ductility at low temperatures in a flat weight drop (DW) type test at -40 ° C. The currently approved test for exhibiting ductility at low temperatures is the burst test, which is more effective for exhibiting brittleness. Most of the examples shown in these documents, alleged to be ductile after the DW test, do not actually show ductile behavior at low temperatures in burst tests and are therefore government regulations (eg, US DOT). It is believed that due to the lack of compliance with, it would not be suitable for certain airbag air pump applications.

  Patent Document 3 is said to cover only steel for use in manufacturing an electric resistance welded pipe (ERW method) (see Patent Document 3). The claims include various aspects of the ERW process and optional heat treatment for annealing or quenching and tempering, optional hidden cold drawing, optional hidden heat treatment (annealing). Or rapid cooling and tempering). This document deals only with two different and very common steel chemistries, one of which is a low carbon steel and the other describes general constraints on various alloying elements. This document does not suggest the possibility of quenching only. Various examples have been given for quenching and tempering materials, but the resulting mechanical properties are relatively low. The maximum result achieved is 852 MPa (123 ksi) in quench and temper test # 18.

  Steel "Chemistry" shown in each of Patent Documents 1, 2, and 3 by Sumitomo as well as the chemistry identified later in Patent Document 4 or the continued literature issued as Patent Document 5 are actually from a long time ago before 1990 Defines a wide range of steels, including SAE 1010 general purpose steels manufactured and sold in the United States (see patent documents 1, 2, 3, 4, 5). Applicants have for several years SAE 1010 steel grades manufactured by modern technology, as described in the application, usually have an amount of P of less than 0.025 and an amount of S of less than 0.01. Knows to compensate.

  Further literature describing the state of the art in steel for air bag applications includes various published pending publications including US Pat. . These documents do not suggest any advantage as taught herein from extremely rapid induction austenitization and hidden ultra-rapid water quenching, and even use only such rapid quenching, And it does not suggest not using a tempering process after that. Further, Patent Document 2 discloses chemistry that overlaps with Patent Document 4 with only a slightly lower maximum value of P (0.02) and a slightly higher maximum value of S (0.02). (See Patent Documents 2 and 4). Although Patent Document 9 broadly suggests the possibility of quenching without tempering, claims 6 and 7 do not state the need for quenching to achieve the claimed mechanical properties, but instead The claim requires at least two types of heat treatment (see Patent Document 9).

  Airbag air pumps for vehicle occupant restraint systems are required to meet strict structural and functional standards. Therefore, strict procedures and tolerances are imposed on the manufacturing process. On-site experience shows that the industry has been successful in meeting past structural and functional standards, but at the same time, continued reductions in manufacturing costs are also important, but to meet evolving requirements There is a need for improved and / or new properties.

  In many vehicles today, airbags or auxiliary restraint systems are important safety devices. In the past, airbag systems were of the type that used explosive chemicals, but they were expensive, and recently due to environmental and reuse issues, steel tubes filled with argon gas etc. A new type of air pump has been developed that uses the resulting accumulator, and this type is increasingly used.

  The accumulator is usually a container that holds high-pressure gas or the like that is blown into an air bag in the event of a car crash in one or many stages of rupture. Therefore, a steel pipe used as such an accumulator must be stressed at a high stress rate in a very short time. Therefore, the steel pipe is required to have excellent dimensional accuracy, excellent workability and weldability compared to a simple structure such as a normal pressure cylinder, and among others, high strength, Must have good toughness and resistance to rupture. Dimensional accuracy is also important to ensure that a very accurate volume of gas is blown into the airbag.

  Since the accumulator is formed into a finished shape after the tube is manufactured, the property of room temperature molding is very important in the tubular member used for manufacturing the accumulator. Different shapes depending on the shape of the container will be obtained by room temperature molding. It is important to obtain a pressure vessel free from cracks and surface defects after cold forming. It is also important to have very good toughness, even at low temperatures after cold forming.

The steel disclosed herein has very good weldability and does not require preheating prior to welding or heat treatment after welding for the application of airbag accumulators. Formula to obtain the required weldability,
Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15
The carbon equivalent defined by must be less than about 0.63%. As Ceq decreases, weldability improves. In a preferred embodiment of the present invention, the carbon equivalent as defined above is less than about 0.60%, preferably less than about 0.56%, and most preferably about 0.52 to better ensure weldability. %, Or even less than about 0.48%.

  To produce a gas container, the cold drawn tube produced according to the present invention is lengthened using different known methods (such as pressure welding, swaging, etc.) to obtain the desired shape. And then molded at room temperature. Alternatively, a welded tube could be used. The end cap and diffuser are then welded to both ends of the vessel by any suitable method, such as friction welding, gas tungsten arc welding, or laser welding, to produce an accumulator. These weldments are of significant importance and therefore require considerable effort and, in certain cases, tests to ensure weld integrity throughout the pressure vessel and airbag deployment. It has been recognized that these weldments can crack or break and thus pose a risk to the integrity of the accumulator and possibly the operation of the airbag.

  Air pumps are tested to ensure that they retain their structural integrity during airbag deployment. One such test is a so-called burst test. This is a destructive type test where the canister is subjected to an internal pressure significantly higher than expected during use in normal operation, ie during deployment of the airbag. In this test, the air pump is subjected to increasing internal pressure until rupture occurs.

  Considering the results of burst tests and studying test canister specimens from these tests, fracture occurs by different alternative methods: ductile fracture, brittle fracture and sometimes a combination of these two modes. Was found. It was observed that in ductile fracture, an outward burst (as would be indicated by a bursting bubble), exemplified by an open bulge, occurred. The ruptured surface has an inclination of about 45 degrees with respect to the outer surface of the tube and is localized in the main region. On the other hand, in brittle fracture, a non-arresting vertical crack along the length of the air pump is shown, indicating a fragile region in the material. In this case, the fracture surface is perpendicular to the outer surface of the tube. These two types of fractures have a unique surface when observed under a scanning electron microscope,-dents are characteristic of ductile fracture, while cracks are brittle.

Occasionally, a combination of these two failure modes is observed, and a fragile fracture can propagate from a ductile fracture. The entire system, including airbag air pumps, can be used in vehicles operating in very different climates, so the material is ductile over a wide range of temperatures from very cold to warm. It is important to show movements.
JP 10-140249 A [Application date, November 5, 1996] JP-A-10-140283 [Application date November 12, 1996] Japanese Patent Laid-Open No. 13-49343 [Application date: October 8, 1999] U.S. Pat. No. 6,878,219, Kondo et al. US Patent No. 2005/0039826 US Pat. No. 6,386,583, Erike US 2004/0074570 US 2005/0061404 Specification US 20020033591

SUMMARY OF THE INVENTION First, the present invention provides a very high tensile strength (minimum UTS 145 ksi), and preferably a very high tensile strength (minimum UTS 160 ksi, and possibly 175 ksi or 220 ksi), and as a result, The target is specific new low-carbon alloy steels suitable for cold forming with high burst pressure. In addition, the steel has excellent ductility behavior at -60 ° C., ie at temperatures as low as −60 ° C. and possibly as low as −100 ° C., with a transition temperature from ductility to brittleness (DBTT). It has toughness.

  Secondly, the present invention is also directed to a method of manufacturing such a steel pipe which essentially comprises a novel rapid induction austenitization / fast quench / no tempering method. In the preferred method, any tempering step is performed to produce a low carbon alloy steel tube suitable for cold forming, having a very high tensile strength (up to UTS 145 ksi-220 ksi) and consequently a very high burst pressure. A very rapid induction austenitization is used, with an ultra-rapid water quenching step to eliminate. Furthermore, the steel is excellent at low temperatures, with a ductile behavior guaranteed at −60 ° C., ie below −60 ° C. and possibly even at a low temperature of −100 ° C., the ductile to brittle transition temperature (DBTT). Toughness.

  The materials of the present invention have particular use in components for containers of components of automotive restraint systems, one example of which is an automotive airbag air pump. The chemicals used to make each of the steels disclosed herein are novel and will subsequently have Steel A, Steel B, Steel C, Steel, each having the composition summarized in Table I below. Will be identified as D and Steel E:

  The test results using each of these steels in a new rapid induction austenitization / fast quench / no tempering process are surprising among the five steel compositions as summarized in Table II below. Showed different results:

  Preferred embodiments of the invention are described in detail below, by way of example only, with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS While the invention may be embodied in various forms, it will be understood that this disclosure can be considered as illustrative of the invention and is not intended to limit the invention to the particular embodiments shown. Thus, presently preferred embodiments will be described below.

  The present invention is directed to a steel pipe used in a pressure vessel of a storage gas air pump. More specifically, the present invention provides a seamless pressure that has a guaranteed ductile movement at the transition temperature from ductility to brittleness at −60 ° C., ie less than −60 ° C. and possibly even at a low temperature of −100 ° C. Covers low carbon, super high strength steel grades for container applications.

  More specifically, the present invention is directed to chemical compositions and processes for obtaining seamless steel pipes that can be used to manufacture air pumps.

The following is a schematic representation of the process for making seamless, low-carbon, ultra-high strength steel:
1. Steel making,
2. Cast steel,
3. Hot rolling of pipes,
4). Hot rolling hollow finishing operation,
5. Cold drawing,
6). Austenite by rapid cooling (without tempering),
7). It could be a cold drawing tube finishing operation.

  One of the main objectives of the steelmaking process is to refine iron by removing carbon, silicon, sulfur, phosphorus and manganese. In particular, sulfur and phosphorus damage steel because they degrade the mechanical properties of the material. In basic steelmaking operations, ladle metallurgy is used before or after the basic process to perform a specific refining process that allows more rapid processing.

The steelmaking process is in turn carried out under very clean practices in order to obtain very low sulfur and phosphorus contents which are important for obtaining the high toughness required for the product. Therefore, inclusion level objectives of Level 2 and below—thin series—and Level 1 and below—dark series have been imposed, following the guidelines of ASTM E45 Standard-Worst Field Method (Method A). In a preferred embodiment of the present invention, the maximum microinclusion content measured according to the above standard is:

Must.

  Furthermore, a very clean implementation makes it possible to obtain an oversize inclusion content with a size of 30 μm or less. The content of these inclusions is obtained by limiting the total oxygen content to 20 ppm.

  A very clean practice in secondary metallurgy is performed by bubbling an inert gas in a ladle furnace to raise inclusions and impurities. Generation of fluid slag capable of absorbing impurities and inclusions and modification of inclusion size and shape by addition of SiCa to liquid steel produces high quality steel with low inclusion content.

Examples using low carbon alloy steels The chemical composition of the resulting steels is as follows, where “%” means “mass percent” respectively.

Carbon (C)
C is an element that increases the strength of steel at low cost. If the content is less than 0.06%, it is difficult to obtain a desired strength. On the other hand, when steel contains C exceeding 0.18%, normal temperature workability, weldability and toughness are reduced. Therefore, the range of C content is 0.06% to 0.18%. A preferred range for the C content is 0.07% to 0.12%, and an even more preferred range is 0.10 to 0.12%.

Manganese (Mn)
Mn is an effective element for increasing the hardenability of steel, and therefore it increases strength and toughness. If the content is less than 0.3%, it is difficult to obtain the desired strength, while if it exceeds 1.5%, the binding structure becomes prominent and the toughness decreases. Therefore, the Mn content is 0.3% to 1.5%, and the preferred Mn range is 0.60 to 1.40%.

Silicon (Si)
Si is an element that has a deoxidizing effect during the steel making process and further increases the strength of the steel. If the silicon content is less than 0.05%, the steel is susceptible to oxidation, whereas if it exceeds 0.50%, both toughness and workability are reduced. Accordingly, the Si content is 0.05% to 0.5%, and the preferred Si range is 0.05% to 0.40%.

Sulfur (S)
S is an element that decreases the toughness of steel. Therefore, the S content is limited to a maximum of 0.015%. A preferred maximum is 0.010%.

Phosphorus (P)
P is an element that decreases the toughness of steel. Accordingly, the P content is limited to a maximum of 0.025%. A preferred maximum is 0.02%.

Nickel (Ni)
Ni is an element that increases the strength and toughness of steel, but is very expensive, so for reasons of price, Ni is limited to a maximum of 0.70%. A preferred maximum is 0.50%.

Chrome (Cr)
Cr is an effective element for increasing the strength, toughness and corrosion resistance of steel. If it exceeds 1%, the toughness of the weld zone is significantly reduced. Therefore, the Cr content is limited to a maximum of 1.0%, and the preferred maximum Cr content is 0.80%.

Molybdenum (Mo)
Mo is effective in increasing the strength of steel and is an element that serves to delay softening during tempering, but is very expensive. Therefore, the Mo content is limited to a maximum of 0.7%, and the preferred maximum Mo content is 0.50%.

Vanadium (V)
V is an element that is effective in increasing the strength of steel even when added in a small amount, and delays softening during tempering. However, this alloy iron is expensive and forces the need to reduce the maximum content. Therefore, V is limited to a maximum of 0.3%, and a preferable maximum value is 0.20%.

Preferred ranges for other elements not listed above are as follows:
Element weight%
Aluminum up to 0.10%
Niobium up to 0.06%
Sn up to 0.05%
Sb up to 0.05%
Pb up to 0.05%
As up to 0.05%.

The residual elements in a ladle of steel used to make tubes or chambers must be:
Sn + Sb + Pb + As ≦ maximum 0.15% and S + P ≦ 0.025.

  The next step is steel casting to produce a solid steel rod that can be penetrated and rolled to form a seamless steel pipe. The steel is cast in a steel shop into round, non-hollow billets with a uniform diameter along the steel axis.

  A non-hollow cylindrical steel slab of ultra-highly clean steel is heated to a temperature of about 1200 ° C. to 1300 ° C., at which point it undergoes a rolling mill process. Preferably, the steel slab is heated to a temperature of about 1250 ° C. and then passed through a rolling mill. The billet is preferably penetrated using the known Manssmann method, then the outer diameter and wall thickness are substantially reduced, while the length is substantially increased during hot rolling. . For example, a 148 mm outer diameter non-hollow bar is hot rolled into a 48.3 mm outer diameter hot rolled tube with a wall thickness of 3.25 mm.

  The rate of reduction of the cross-sectional area, measured as the ratio of the cross-sectional area of the non-hollow steel slab to the cross-sectional area of the rolled tube, is important for obtaining the refined microstructure necessary to obtain the desired mechanical properties. Accordingly, the minimum cross-sectional area reduction rate is about 15: 1, and the preferred and most preferred minimum cross-sectional area reduction rates are about 20: 1 and about 25: 1, respectively.

  The seamless hot-rolled tube of ultra-high clean steel so produced is cooled to room temperature. An ultra-high clean steel seamless hot-rolled tube so produced has a substantially uniform wall thickness both around the tube and longitudinally along the tube axis.

  The hot-rolled tube then goes through different finishing steps, for example cut into lengths of 2 to 4 pieces and cut off its ends, if necessary straightened with a known rotary linearizer and electromagnetic testing Or it is non-destructively tested by one or more different known methods such as ultrasonic testing.

  Next, the condition of the surface of each piece of the hot-rolled tube is appropriately adjusted for drawing at room temperature. This conditioning can be accomplished by dipping in an acid solution and a suitable combination of known zinc phosphate and sodium esterate combinations or lubricants such as reactive oils. Applying a layer. After adjusting the surface conditions, room temperature drawing is performed by drawing the seamless pipe through an external die having a diameter smaller than the outer diameter of the pipe to be drawn. In most cases, the inner surface of the tube is also supported by an internal mandrel secured to one end of the rod so that the mandrel remains close to the die during withdrawal. This drawing operation is performed without the need to preheat the tube above room temperature.

  A seamless tube is so drawn at room temperature at least once so that each pass reduces both the outer diameter and the wall thickness of the tube. The cold drawn steel pipe so produced has a uniform outer diameter and a uniform wall thickness along the tube axis, both around the tube and longitudinally along the tube axis. Such cold drawn tubes preferably have an outer diameter between 10 and 70 mm and a wall thickness of preferably 1 to 4 mm.

  The cold draw tube is then passed through at least the upper austenitizing temperature, or Ac3 (about 880 ° C. for the specific compounds disclosed herein), but preferably above about 920 ° C. and about 1050 ° C. Heat treatment in an austenitizing furnace at a temperature below. This maximum austenitizing temperature is imposed in order to avoid crystal coarsening. This step can be carried out either in a fuel furnace or in an induction furnace, but is preferably carried out in the latter. In-furnace travel time is highly dependent on the type of furnace used. It has been found that the high surface quality required by this application is better obtained when an induction furnace is used. This is due to the nature of the induction process, which involves a very short migration time that prevents oxidation from taking place. Preferably, the austenitizing heating rate is at least about 100 ° C per second, more preferably at least about 200 ° C per second. Very high heating rates and the resulting very short heating times are important for obtaining very fine crystalline microstructures which in turn guarantee the necessary mechanical properties.

  In addition, an appropriate filling factor, defined as the ratio of the circular area defined by the outer diameter of the tube to the circular area defined by the inner diameter of the induction furnace coil, is important to obtain the required high heating rate. It is. The minimum fill factor is about 0.16 and the preferred minimum fill factor is about 0.36.

  At or near the exit area of the furnace, the tube is quenched with a suitable quench liquid. The quench liquid is preferably water or a water base quench solution. The tube temperature rapidly decreases to ambient temperature, preferably at a rate of at least about 100 ° C. per second, more preferably at a rate of at least about 200 ° C. per second. This extremely high cooling rate is important in order to obtain a complete microstructure transformation.

  Next, in a method where a tempering step is used, the steel pipe is tempered using a suitable temperature and cycle time at a temperature below Ac1. Preferably, the tempering temperature is between about 400-600 ° C and more preferably between about 450-550 ° C. Alternatively, the tempering temperature can be between 200C and 600C, and more preferably between about 250C and 550C. The soaking time must be long enough to ensure very good temperature uniformity, but if it is too long, the desired mechanical properties cannot be obtained. This tempering step is preferably performed in a protective reducing or neutral atmosphere to avoid decarburization and / or oxidation of the tube.

In the preferred method, the tempering step is avoided and only rapid quenching using water or a water base solution as described above is used. In order to achieve rapid quenching, the following apparatus is preferred but not essential. An induction furnace with a quenching line with a total capacity of 2200 kg per hour and then a maximum power of induction source set to 500 Kw. The head quencher uses 42 lines with 12 nozzles on each line. The water quench flow rate is adjusted to a range of 10-60 m ³ per hour and the tube advance speed is controlled to 5-25 meters per minute. In addition, the next pinch roller is set to cause rotation on the tube.

  The super high strength steel pipes so produced are passed through different finishing steps, straightened with known rotary linearizers, and tested non-destructively by one or more different known methods . Tubes for this type of application should preferably be tested by both known ultrasonic and electromagnetic methods.

  The heat-treated tube can be chemically treated to obtain a tube with the desired appearance and very low surface roughness. For example, a tube could be immersed in sulfuric acid and hydrochloric acid solution, phosphorylated using zinc phosphate, and oil treated using petroleum based oil, water based oil or mineral oil. Let's go.

The steel pipe obtained by the method described in the first or second has the following minimum mechanical properties:
Yield Strength (Approximately 110 ksi)
(758 MPa)
Tensile Strength Minimum of about 145 ksi
(1000 MPa)
Elongation Minimum 9%

  Yield strength, tensile strength and elongation can be carried out according to the methods described in standard ASTM E8. For the tensile test, a full-size specimen is preferred for evaluating the entire tubular portion.

  The flattening test must comply with the conditions of 49 CFR, standard DOT 39 of paragraph 178.65. Therefore, the tube piece must not crack when flattened with a V-shaped tool at an angle of 60 degrees until the opposite side is 6 times the thickness of the tube wall. This test is fully satisfied by the developed steel.

  In order to obtain a good balance between strength and toughness, the prior (sometimes referred to as former) austenite grain size is measured according to the ASTM E-112 standard, preferably 7 or less, And more preferably it must be 9 or less. This is achieved thanks to a very short heating cycle during the austenitization period.

  The steel pipe obtained by the above method must have the above properties in order to comply with the conditions described for the present invention.

  Industry demands continue to force roughness conditions to lower values. The present invention has a good visual appearance, for example, with a finished tube surface finish of up to 3.2 microns on both the outer and inner surfaces. This condition is obtained by cold drawing at different stages of the process, short austenitizing time, reduction or tempering of a neutral atmosphere and appropriate surface chemical conditioning.

  The hydroburst pressure test must be performed, for example, by sealing the end of the tube section by welding a flat steel plate to the tube end. It is important that the 300 mm tube piece remains unconstrained so that all the hop stress can develop. Pressurization of the tube section may be performed by pumping out oil, water, alcohol or mixtures thereof.

  The pressure condition of the burst test depends on the tube size. During burst testing, the ultra high strength steel seamless tube has a ductile motion guaranteed at -60 ° C. Tests performed on the manufactured samples show a ductile to brittle transition temperature below −60 ° C. and a guaranteed ductile movement of −60 ° C.

  The present inventor has found that instead of the Charpy impact test (according to ASTM E32), a burst test performed at both ambient and low temperatures is a much more representative and effective test. This is due to the fact that relatively thin wall thicknesses and small outer diameters are used in these products, so standard ASTM specimens for Charpy impact testing cannot be machined from the tube in the transverse direction. Furthermore, in order to obtain a Charpy impact probe smaller than this standard, a flattening deformation must be applied to the curved tube probe. This has a significant effect on the mechanical properties of the steel, in particular the impact strength. Therefore, typical impact test results cannot be obtained by this method.

Examples Using Alternative Low Carbon, Low Alloy Steel Applicants have found that rapid quenching without tempering is an important aspect of the present invention. When processed with specific heating and rapid quenching, steels that are lower alloys and less expensive than prior art compounds can meet or exceed the standards previously discussed herein.

  As defined above, the new steels A, B, C, D and E use the preferred method in which a very rapid induction furnace austenitization with fast quenching is used instead of adding a tempering step. Instead of the steel analyzed. Surprisingly, if a controlled test in which a rapid quenching, i.e. a normal quenching process, or a tempering process as described above is used, is performed on certain of these new steels, which is not fast. The test showed significantly inferior features.

According to the preferred method, the process was fast quenched using alternatives including cheaper steel and without tempering. The parameters used for the rapid quench test on the steel E sample were:
40m ³ / hr water flow, 20m / min tube advance rate, 80% induction power, austenitizing temperature of 880-940 ° C, target 920 ° C, martensitic transformation on OD surface and core material Admitted.

  FIG. 1 shows the core material with 100% martensitic transformation for steel E.

  Steel E, which has a chemical structure similar to low alloy SAE 1010 grade steel, did not achieve the lowest expected value when subjected to rapid quenching.

  The test results were as follows:

  Similarly, a burst test at low temperature (−60 ° C.) was performed to observe the movement and type of cracks. FIG. II shows a test burst sample of Steel E. Both showed a ductile movement.

  A control test on steel E with normal quenching process was performed and the results were as follows:

  FIG. III shows the core structure for steel E using a normal quenching process. Some ferrite structure is observed along the wall thickness.

  Steel D was found very promising because of its high performance for the indicated price value. Steel D was selected to produce the tube according to the preferred method. The measured chemical composition of the sample of Steel D used for the rapid quench test was as follows:

The parameters used for the rapid quench test on the steel D sample were:
The rapid cooling process was performed by controlling the austenite temperature to 920 to 940 ° C.
Water flow 40m ³ / hour,
Tube forward speed 10m / min,
Induction device power, 62% of total capacity (500Kw),
The rotation on the tube was given with a 17 ° pinch roll angle.

  The results of the rapid quenching on the steel D sample were as follows:

  FIG. IV shows the microstructure of high-speed quenched steel D showing 100% martensite and a fully quenched transformation.

  Similarly, a burst test was performed at low temperature (−60 ° C.) to observe the movement and type of cracks. FIG. V shows a test burst sample of Steel D. Both showed a ductile movement.

  A control test on steel D with a normal quenching process was performed and the results are as follows:

  FIG. VI shows the core structure of Steel D using a normal quenching process.

  Steel B was selected to produce the tube according to the preferred method. The measured chemical composition of the steel B sample used in the rapid quench test was as follows:

The parameters used for the rapid quench test on the steel B sample were:
The quenching step was performed while controlling the austenite temperature at 920 to 940 ° C.
Water flow 40m ³ / hour,
Pipe forward speed 10m / min Inductor power, 70% of total capacity (500Kw)
The rotation on the tube was given with a 17 ° pinch roll angle.

  The results of the rapid quenching on the steel B sample were as follows:

  Similarly, a low temperature (−60 ° C.) burst test was performed on Steel B to observe crack motion and type, both exhibiting ductile motion.

  Steel A was selected to produce the tube according to the preferred method. The measured chemical composition of the sample of Steel A used for the rapid quench test was as follows:

The parameters used for the rapid quench test on the steel A sample were:
The quenching step was performed while controlling the austenite temperature at 920 to 940 ° C.
Water flow 50m ³ / hour,
Tube forward speed 20m / min,
Induction device power, 90% of total capacity (500Kw),
The rotation on the tube was given with a 17 ° pinch roll angle.

  The results of the rapid quenching on the steel A sample were as follows:

  Similarly, low temperature (−60 ° C. and −100 ° C.) burst tests were performed on Steel A to observe crack motion and type, both exhibiting ductile motion.

Control test with fast quench using alternative low-priced steel and with tempering process The preferred steel D sample was found to give surprising mechanical values when using fast quench according to the preferred method. In addition, tempering was performed to determine the effect of adding tempering on the mechanical properties.

  The tempering heat treatment was carried out at 580 ° C. for a total time of 15 minutes. The UTS average was 116 Ksi (805 MPa), which did not satisfy the expected value.

  35 Although preferred embodiments of our invention have been shown and described in order to comply with the description and enablement requirements of USC §112, the scope of the present invention is not limited to any of the described embodiments. It can be seen that it is defined only by the scope of the claims.

The core microstructure for fast quenching on steel E is shown. The burst test at −60 ° C. for rapid quenching on steel E is shown. The microstructure for normal quenching on Steel E is shown. 3 shows the microstructure of a rapidly quenched core on Steel D. The burst test at -60 degreeC with respect to the rapid quenching on the steel D is shown. The microstructure for normal quenching on steel D is shown.

Claims (48)

Essentially, by weight, from about 0.06% to about 0.18% carbon, from about 0.5% to about 1.5% manganese, from about 0.1% to about 0.5% silicon, Up to about 0.015% sulfur, up to about 0.025% phosphorus, up to about 0.50% nickel, from about 0.1% to about 1.0% chromium, from about 0.1% to about 1. 0% molybdenum, about 0.01% to about 0.10% vanadium, about 0.01% to about 0.10% titanium, about 0.05% to about 0.35% copper, about 0.0. Low carbon alloy steel pipe comprising 010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and balance iron and incidental impurities Because
A low carbon alloy steel pipe having a tensile strength of at least about 145 ksi and a ductile to brittle transition temperature of less than -60 ° C.   The steel tube is essentially about 0.07% to about 0.12% carbon, about 1.00% to about 1.40% manganese, about 0.15% to about 0.35% by weight. Silicon, up to about 0.010% sulfur, up to about 0.015% phosphorus, up to about 0.20% nickel, from about 0.55% to about 0.80% chromium, from about 0.30% About 0.50% molybdenum, about 0.01% to about 0.07% vanadium, about 0.01% to about 0.05% titanium, about 0.15% to about 0.30% copper, The low carbon alloy of claim 1 comprising from about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Steel pipe.   The steel tube is essentially about 0.08% to about 0.11% carbon, about 1.03% to about 1.18% manganese, about 0.15% to about ~ 0.35% by weight. Silicon, up to about 0.003% sulfur, up to about 0.012% phosphorus, up to about 0.10% nickel, from about 0.63% to about 0.73% chromium, from about 0.40% About 0.45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper, The low carbon alloy of claim 1 comprising from about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Steel pipe.   The low carbon alloy steel pipe of claim 1, wherein the steel pipe has a yield strength of at least about 125 ksi.   The low carbon alloy steel pipe of claim 1, wherein the steel pipe has a yield strength of at least about 135 ksi.   The low carbon alloy steel pipe of claim 1, wherein the steel pipe has an elongation at break of at least about 9%.   The low carbon alloy steel pipe of claim 1, wherein the steel pipe has a hardness of about 40 HRC or less.   The low carbon alloy steel pipe of claim 1, wherein the steel pipe has a hardness of about 37 HRC or less.   The steel pipe has a carbon equivalent of less than about 0.63%, where the carbon equivalent is determined according to the formula: Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15: The low carbon alloy steel pipe according to claim 1.   The low carbon alloy steel pipe of claim 9, wherein the steel pipe has a carbon equivalent of less than about 0.60%.   The low carbon alloy steel pipe of claim 9, wherein the steel pipe has a carbon equivalent of less than about 0.56%.   2. The steel pipe of claim 1, comprising a maximum of microinclusion of level 2 or less-thin series-and level 1 or less-dense series-measured according to the ASTM E45 Standard-Worst Field method (Method A). Low carbon alloy steel pipe. Steel pipes are the following:
The low carbon alloy steel pipe of claim 1, comprising a maximum trace inclusion measured according to the ASTM E45 Standard-Worst Field method (Method A).   14. The low carbon alloy steel pipe of claim 13, wherein an oversize inclusion content of a size of 30 [mu] m or less is obtained.   15. The low carbon alloy steel pipe of claim 14, wherein the total oxygen content is limited to 20 ppm.   The low carbon alloy steel pipe of claim 1, wherein the pipe has a seamless configuration.   A pressure vessel for a storage gas air pump comprising the low carbon alloy steel pipe of claim 1.   An air pump for an automobile airbag comprising the low carbon alloy steel pipe according to claim 1.   Essentially, by weight, from about 0.08% to about 0.11% carbon, from about 1.03% to about 1.18% manganese, from about 0.15% to about 0.35% silicon, Up to about 0.003% sulfur, up to about 0.012% phosphorus, up to about 0.10% nickel, about 0.63% to about 0.73% chromium, about 0.40% to about 0.00. 45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper, about 0.0. A low carbon alloy steel pipe comprising 010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities, A proof stress of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least about 9%, 37HRC have the following hardness, and has a transition temperature to brittle from -60 ° C. of less than ductility, low carbon alloy steel.   20. The low carbon alloy steel pipe of claim 19, wherein the pipe has a seamless shape.   20. A preservative gas air pump pressure vessel comprising the low carbon alloy steel pipe of claim 19.   An air pump for an automobile airbag comprising the low carbon alloy steel pipe of claim 19.   The following steps: essentially from about 0.06% to about 0.18% carbon, from about 0.5% to about 1.5% manganese, from about 0.1% to about 0.5 by weight. % Silicon, up to about 0.015% sulfur, up to about 0.025% phosphorus, up to about 0.50% nickel, from about 0.1% to about 1.0% chromium, about 0.1% ~ About 1.0% molybdenum, about 0.01% to about 0.10% vanadium, about 0.01% to about 0.10% titanium, about 0.05% to about 0.35% copper. A length of steel material consisting of about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Producing a tube; subjecting the steel tube to a cold drawing process to obtain the desired dimension; at a rate of at least Ac3 at a heating rate of at least about 100 ° C. per second Austenitized by heating a cold drawn steel tube in an induction type austenitizing furnace to a degree; in the quenching liquid after the heating step, at a cooling rate of at least about 100 ° C. per second until the tube reaches near ambient temperature A method of producing a length of steel pipe for a storage gas air pump pressure vessel comprising: quenching the steel pipe; and tempering the steel pipe after the quenching step at a temperature less than Ac1 for about 2 to 30 minutes. .   The resulting steel pipe is essentially about 0.07% to about 0.12% carbon, about 1.00% to about 1.40% manganese, about 0.15% to about 0 by weight. .35% silicon, up to about 0.010% sulfur, up to about 0.015% phosphorus, up to about 0.20% nickel, from about 0.55% to about 0.80% chromium, 30% to about 0.50% molybdenum, about 0.01% to about 0.07% vanadium, about 0.01% to about 0.05% titanium, about 0.15% to about 0.30% 24. of copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Method.   The resulting steel pipe is essentially about 0.08% to about 0.11% carbon, about 1.03% to about 1.18% manganese, about 0.15% to about 0 by weight. .35% silicon, up to about 0.003% sulfur, up to about 0.012% phosphorus, up to about 0.10% nickel, about 0.63% to about 0.73% chromium, about 0.03%. 40% to about 0.45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% 24. of copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Method.   24. The method of claim 23, wherein the finished steel pipe has a proof stress of at least about 125 ksi.   24. The method of claim 23, wherein the finished steel pipe has a proof stress of at least about 135 ksi.   24. The method of claim 23, wherein the finished steel pipe has a tensile strength of at least about 145 ksi.   24. The method of claim 23, wherein the finished steel tube has an elongation at break of at least about 9%.   24. The method of claim 23, wherein the finished steel pipe has a hardness of about 40 HRC or less.   24. The method of claim 23, wherein the finished steel pipe has a hardness of about 37 HRC or less.   24. The method of claim 23, wherein the finished hardness has a ductile to brittle transition temperature of less than -60C.   24. The method of claim 23, wherein in the austenitizing heating step, the steel pipe is heated to a temperature between about 920-1050 <0> C.   34. The method of claim 33, wherein in the austenitizing heating step, the steel pipe is heated at a rate of at least about 200 ° C per second.   24. The method of claim 23, wherein the steel pipe is cooled at a rate of at least about 200 ° C. per second in the quenching step.   24. The method of claim 23, wherein the steel pipe is tempered at a temperature between about 400-600 [deg.] C. in the tempering step.   38. The method of claim 36, wherein in the tempering step, the steel pipe is tempered for about 4 to 20 minutes.   24. The method of claim 23, further comprising a finishing step in which the tempered steel pipe is pickled, phosphorylated and oiled.   The following steps: essentially from about 0.08% to about 0.11% carbon, from about 1.03% to about 1.18% manganese, from about 0.15% to about 0.35 by weight. % Silicon, up to about 0.003% sulfur, up to about 0.012% phosphorus, up to about 0.10% nickel, from about 0.63% to about 0.73% chromium, about 0.40% About 0.45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper. A length of steel material consisting of about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements and residual iron and incidental impurities. Manufacture the tube; subject the steel tube to cold drawing to obtain the desired dimension; at a heating rate of at least about 200 ° C. per second Austenitizing by heating a cold drawn steel tube in an induction type austenitizing furnace to a temperature between about 920-1050 ° C; after the heating step, the tube is brought to near ambient temperature at a cooling rate of at least about 200 ° C per second. Quenching the steel pipe in a water base quench solution until it reaches; and after the quenching step, tempering the steel pipe at a temperature between about 450-550 ° C. for about 4-20 minutes, pickling the tempered steel pipe A finished steel pipe, wherein the finished steel tube has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least 9%, a hardness of about 37 HRC or less, − Produced a length of steel pipe for preserving gas air pump pressure vessel with transition temperature from ductility to brittleness below 60 ° C and good surface appearance How to.   The following steps: essentially from about 0.06% to about 0.18% carbon, from about 0.3% to about 1.5% manganese, from about 0.05% to about 0.5 by weight. % Silicon, up to about 0.015% sulfur, up to about 0.025% phosphorus and at least one of the following elements: up to about 0.30% vanadium, up to about 0.10% aluminum, about 0 0.06% niobium, up to about 1% chromium, up to about 0.70% nickel, up to about 0.70% molybdenum, up to about 0.35% copper, up to about 0.15% residual elements And producing a length of tubing from the steel material consisting of the remaining iron and incidental impurities; subjecting the steel pipe to a cold drawing process to obtain the desired dimension; heating the cold drawn steel pipe to at least about 100 ° C. per second Induction type austenite at a temperature of at least Ac3 Austenitizing by heating in a calcination furnace; comprising, after the heating step, quenching the steel tube in a quenching liquid at a cooling rate of at least about 100 ° C. per second until the tube reaches approximately ambient temperature; Producing a length of steel pipe for a storage gas air pump pressure vessel where the steel pipe has a tensile strength of at least about 145 ksi and a transition temperature from ductility to brittleness of less than −60 ° C. how to.   The resulting steel tube is essentially about 0.07% to about 0.12% carbon, about 0.60% to about 1.40% manganese, about 0.05% to about. 40% silicon, up to about 0.010% sulfur, up to about 0.02% phosphorus and at least one of the following elements: up to about 0.20% vanadium, up to about 0.07% aluminum, about Up to 0.04% niobium, up to about 0.8% chromium, up to about 0.50% nickel, up to about 0.50% molybdenum, up to about 0.35% copper, up to about 0.15% 41. The method of claim 40, wherein the steel tube has a tensile strength of at least about 160 ksi and a ductile to brittle transition temperature of less than -60 ° C. The steel pipe has a carbon equivalent of less than about 0.52%, and the carbon equivalent is represented by the formula:
Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15:
41. The method of claim 40, determined according to: The steel pipe has a carbon equivalent of less than about 0.48%, and the carbon equivalent is represented by the formula:
Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15:
42. The method of claim 41, determined according to:   41. The method of claim 40, wherein the finished steel pipe has an elongation at break of at least about 9%.   41. The method of claim 40, wherein in the austenitizing heating step, the steel pipe is heated to a temperature between about 860-1050 <0> C.   41. The method of claim 40, wherein in the austenitizing heating step, the steel pipe is heated at a rate of at least about 200 ° C per second.   41. The method of claim 40, wherein in the quenching step, the steel pipe is cooled at a rate of at least about 200 ° C per second.   The following steps: essentially from about 0.07% to about 0.12% carbon, from about 0.60% to about 1.40% manganese, from about 0.05% to about 0.40 by weight. % Silicon, up to about 0.010% sulfur, up to about 0.02% phosphorus, up to 0.20% vanadium, up to about 0.07% aluminum, up to about 0.04% niobium, about 0 Up to .8% chromium, up to about 0.50% nickel, up to about 0.50% molybdenum, up to about 0.35% copper, up to about 0.15% residual elements and residual iron and incidental A length of tubing is produced from the steel material consisting of impurities; the steel pipe is subjected to a cold drawing process to obtain the desired dimension; the cold drawn steel pipe is about 860-1050 at a heating rate of at least about 200 ° C. per second. Heat in an induction type austenitizing furnace to a temperature between Austenitizing; comprising, after the heating step, quenching the steel pipe in a water based quench solution at a cooling rate of at least about 200 ° C. per second, wherein the finished steel pipe has a tensile strength of at least about 160 ksi; Produces a length of steel pipe for a storage gas air pump pressure vessel having an elongation at break of at least about 9% and a ductile to brittle transition temperature of less than −60 ° C., and preferably less than 100 ° C. how to.