JP2000204438A - Steel pipe excellent in wear resistance characteristic and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe for nitriding excellent in workability and used for parts requiring wear resistance, seizuring resistance, fatigue characteristics such as parts for tools and machine structures and automotive parts. SOLUTION: A steel pipe contg., by weight, 0.0002 to 0.20% C, 0.002 to 1.0% Si, 0.02 to 3.0% M, 0.001 to 0.030% P, 0.001 to 0.050% S, 0.0002 to 0.0100% N, and the balance Fe with inevitable impurities and in addition contg. one or >= two kinds among 0.100 to 2.0% Al, 0.05 to 5.0% Cr, 0.010 to 1.0% V and 0.005 to 1.0% Ti as nitriding promoting elemental groups is worked and formed, and, on the surface of the worked and formed body, a hard nitriding layer is formed. Even in low carbon steel and extra-low carbon steel excellent in workability in itself, sufficient surface hardness and the depth of a hardened layer after nitriding can be obtd. without deteriorating the workability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride, which is excellent in workability and is used for parts requiring wear resistance, seizure resistance and fatigue characteristics, such as tools, parts for mechanical structures, and automobile parts. It is related to steel pipes.

[0002]

2. Description of the Related Art Numerous attempts have been made to improve the wear resistance, seizure resistance and fatigue properties of steel.
As disclosed in JP-A-9-31850 and JP-B-59-50158, steels for nitriding are known. After being formed into a component, the steel is subjected to heat treatment to cause nitrogen to enter the steel and form a hard nitride layer on the surface of the steel. However, such a steel has a drawback that, since a large amount of an alloying element that promotes nitriding is added, there is no workability, and parts must be formed from bar steel or the like by grinding which requires enormous labor and cost. I was Therefore, such steel cannot be applied to parts requiring workability. In addition, low-carbon steels and ultra-low-carbon steels with good workability do not have sufficient surface hardening and hardening depth after nitriding, and have abrasion resistance, seizure resistance, and fatigue characteristics compared to general nitriding steels. Was inferior.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to improve the abrasion resistance, seizure resistance and fatigue properties of a steel pipe using conventional steel for nitriding, resulting in a disadvantage that workability is lost. In steel pipes made of low-carbon steel and ultra-low-carbon steel with excellent workability, the surface hardening after nitriding and the depth of the hardened layer are not sufficient, and it is possible to improve wear resistance, seizure resistance, and fatigue properties. This was done to eliminate the drawback that it could not be done.

[0004]

Means for Solving the Problems The gist of the present invention is that the weight%
C: 0.0002 to 0.20%, Si: 0.002 to 1.0%, M
n: 0.02 to 3.0%, P: 0.001 to 0.030%, S: 0.
001-0.050%, N: 0.0002-0.0100%, balance: Fe
Al: 0.100 to 2.0%, Cr: 0.05 to 5.0
%, V: 0.010 to 1.0%, and Ti: 0.005 to 1.0%.
A steel pipe excellent in wear resistance and workability, characterized in that a hard nitride layer is formed on the surface of the processed body.

Alternatively, C: 0.0002 to 0.20 by weight%
%, Si: 0.002 to 1.0%, Mn: 0.02 to 3.0%, P
: 0.001 to 0.030%, S: 0.001 to 0.050%, N
: 0.0002 to 0.0100% as a basic component system, and Nb: 0.005 to 0.080%, Mo: 0.05 to 0.
5%, B: 0.0003 to 0.0050%, one or more of the following, and the balance: Fe and unavoidable impurities, and in addition, Al: 0.100 to 2.
0%, Cr: 0.05 to 5.0%, V: 0.010 to 1.0%, T
i: 0.005 to 1.0%, one or two or more steel pipes containing therein are worked and formed, and a hard nitride layer is formed on the surface of the processed body. It is in a steel pipe with excellent properties

A feature of the present invention is that, in a conventional steel pipe using low carbon steel or ultra low carbon steel, the surface hardening after nitriding and the depth of the hardened layer are not sufficient, As a result of intensive investigations on the effects of surface hardening and the depth of the hardened layer, even low-carbon steels and ultra-low-carbon steels, which are originally excellent in workability, can be processed by adding additional elements within the component range of the present invention. It has been found that a sufficient surface hardening after nitriding and a depth of a hardened layer can be obtained without impairing the hardness.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reasons for limiting the components of steel in the present invention will be described. If the content of C is less than 0.0002%, the cost for decarburization increases and it becomes uneconomical, so the lower limit is made 0.0002%. On the other hand, if it exceeds 0.20%, the amount of carbides increases and the workability deteriorates. Therefore, the upper limit is 0.20%.

In order to precipitate and fix C and N, the amount of Ti should be not less than {(48/12) × C [%] + (48/14) × N [%]} or the amount of Nb should be {(93/12) ) × C [%] + (93 /
14) 0.8 times or more of × N [%]｝ or when Ti and Nb are added in combination, the amount of Ti is {(48/12) × C [%] +
When it is less than (48/14) × N [%]｝, Nb is 0.8
× (93/12) × C [%] × ｛1- (Ti [%] − (48 /
14) It is desirable to add XN [%]} or more.

If the content of Si is reduced to less than 0.002%, the production cost is increased and the economy is impaired. Therefore, the lower limit is 0.002%, and if it exceeds 1.0%, the workability is deteriorated.
Is the upper limit.

Since reducing Mn to less than 0.02% increases the production cost and impairs economic efficiency, the lower limit is set to 0.02%, and if it exceeds 3.0%, the workability is deteriorated, so the upper limit is 3.0%.

If P is reduced to less than 0.001%, the production cost is increased and the economy is impaired. Therefore, the lower limit is 0.001%, and if it exceeds 0.030%, the workability is deteriorated.
% As the upper limit.

If S is reduced to less than 0.001%, the production cost is increased and the economy is impaired. Therefore, the lower limit of S is 0.001%, and if it exceeds 0.050%, the workability deteriorates.
% As the upper limit.

N is preferably as small as possible.
If the content is less than 0%, manufacturing costs will increase.
When the lower limit is 0002% and the content exceeds 0.0100%, the age hardening property is increased and the workability is deteriorated. Therefore, the upper limit is set to 0.0100%.

Next, the reasons for limiting the contents of the components added as the group for promoting nitriding will be described. Al is an element that promotes nitride formation at the same time as being a deoxidizing element. When used as a nitride formation promoting element, if less than 0.100%,
Since the surface hardening due to nitriding treatment is not enough, wear resistance, seizure resistance, and fatigue characteristics cannot be obtained. If the lower limit is 0.100%, and if it exceeds 2.0%, ductility is deteriorated, and cracks are especially generated during overhanging. Therefore, the upper limit is 2.0%.

If the content of Cr is less than 0.05%, the surface hardening due to nitriding is not sufficient, and the desired wear resistance, seizure resistance and fatigue characteristics cannot be obtained, so the lower limit is 0.05%. 5.0
%, The ductility is degraded, and cracks occur particularly during overhanging. Therefore, the upper limit is 5.0%.

If V is less than 0.010%, the surface hardening due to nitriding is not sufficient, and wear resistance, seizure resistance and fatigue properties cannot be obtained. Therefore, the lower limit of V is 0.010%, and when V exceeds 1.00%, Since the ductility deteriorates and cracks occur particularly during overhanging, the upper limit is 1.0%.

Ti is an element that precipitates solid solution C to secure workability, and is an element that promotes nitride formation.
When used as a nitride formation promoting element, if the content is less than 0.005%, the surface hardening due to nitriding is not sufficient, and the wear resistance, seizure resistance and fatigue characteristics cannot be obtained, so the lower limit is 0.005% and the content exceeds 1.00%. Then, ductility is deteriorated, and cracks occur particularly during overhanging. Therefore, the upper limit is set to 1.00%.

Next, the reasons for limiting the contents of the components to be added as the selectively added element group will be described. If Nb is less than 0.005%, the effect of precipitating and fixing C and N is small, so the lower limit is 0.005%, and if it exceeds 0.080%, the deep drawability deteriorates, so the upper limit is 0.080%.

Mo is an element that is effective for securing strength as a solid solution strengthening element, and is effective for increasing strength without deteriorating corrosion resistance and low-temperature toughness. When the amount is less than 0.05%, the strengthening ability is small. Therefore, 0.05% is set as the lower limit, and if it exceeds 0.50%, the strength is increased more than necessary. Therefore, the upper limit is set to 0.50%.

B is added for the purpose of strengthening the strength of the crystal grain boundaries of steel, which is weakened due to the low carbon component, and for preventing secondary working embrittlement. If B is less than 0.0003%, the effect of preventing secondary working embrittlement is small, so the lower limit of 0.0003% is 0.0050%.
%, The deep drawability deteriorates, so the upper limit is 0.0050%. In addition, since B has a strong affinity with nitride, even in a steel containing a nitride-forming element in the component range of the steel material used in the present invention, the nitriding property of the steel is not hindered, and the steel is further improved. Is also possible.

The addition of Cu and Ni is not an essential condition of the present invention, but the addition of these elements contributes to the increase in strength and the hardenability. Not against the gist. The addition of Ca and Zr for the purpose of controlling the morphology of nonmetallic inclusions does not depart from the gist of the present invention.

Next, a method of manufacturing a steel pipe and a method of utilizing the same will be described. A slab made of a low-alloy steel containing the components described above is formed, and the slab is subjected to hot rolling, or further cold rolling, or further recrystallization heat treatment to produce a steel pipe material. The method for producing the hot-rolled steel sheet is not particularly limited, but in order to improve the workability of the steel sheet, the slab is heated at a temperature of 1050 to 1150 ° C,
Alternatively, it is desirable to wind up at a temperature of 600 ° C. or more to precipitate and fix the carbon contained in the steel. Next, cold-rolled, recrystallized and annealed, and cold-rolled steel sheet
Although the production method is not particularly limited, a structure excellent in deep drawability can be obtained by performing cold rolling at a rolling reduction of 60% or more and recrystallizing at 700 ° C. or more.

Next, the steel pipe material is formed into a circular shape using the steel pipe material, then welded to form a welded steel pipe, and then formed into a predetermined shape, and then subjected to nitriding treatment. A layer is formed (it may be local instead of the entire surface) to improve wear resistance, seizure resistance and fatigue properties. The hard nitride layer refers to an outermost iron-nitrogen compound layer and a hard nitrogen diffusion layer formed inside a steel material. In addition, a hole is made in the material billet, and a seamless steel pipe is used,
The same is true for the case of manufacturing by heat treatment.

As the nitriding treatment, there are various treatment methods such as a gas nitriding treatment, a gas nitrocarburizing treatment, a salt bath nitrocarburizing treatment, an ion nitriding treatment, an oxynitriding treatment and a sulphonitriding treatment. Any processing method may be used. Necessary nitride layer depth (preferably 20 μm or more)
The processing time can be appropriately changed in order to obtain. The thickness of the obtained surface nitride layer may be reduced by means of grinding or the like to adjust the layer thickness or adjust the surface roughness without any problem.

The hardness of the hard nitride layer is desirably about 415 or more by micro Vickers. Although the upper limit hardness is not limited, in the current nitriding technology,
It is about 1500. In addition, the steel pipe and the processed compact obtained by the method of the present invention can be subjected to hot-dip plating and / or electroplating for the purpose of improving corrosion resistance, coating properties, and weldability. Does not deviate. Further, it is of course possible to add various treatments to the steel pipe of the present invention, for example, chromate treatment, phosphate treatment, treatment for consolidating phosphate treatment, lubricity improvement treatment, weldability improvement The present invention does not depart from the scope of the present invention even if a treatment, a resin film treatment or the like is performed, and various treatments can be additionally performed according to necessary characteristics.

[0026]

Examples Nos. 1 to 18 in Table 1 are examples of the present invention.
The slabs of Nos. 1 to 8 are subjected to hot rolling, or further cold rolling, or further recrystallization heat treatment to produce a steel pipe material. The steel pipe material is formed into a circular shape, and then welded and welded. It was a steel pipe. These are expanded, the expansion ratio is measured,
Workability was evaluated. When the expansion ratio was 1.2D or more, the workability was evaluated as good. When the expansion ratio was less than 1.2D, the workability was evaluated as poor. Further, the steel pipe was subjected to a nitriding treatment at 570 ° C. for 4 hours in a mixed atmosphere gas of NH ₃ gas and endothermic gas, followed by oil cooling. Using a micro-Vickers hardness tester, the nitriding property was evaluated with a hardness (Hv) at a load of 100 g at a position 30 μm from the surface.
Each hardness is an average value of five points. No. 19 to 24 in Table 1
Shows a comparative example for the present invention. As is clear from Table 1, it is understood that the steel pipe of the present invention achieves both excellent workability and excellent nitridation, which cannot be obtained in Comparative Examples.

[0027]

[Table 1]

[0028]

According to the present invention, without impairing workability,
A steel pipe having excellent surface hardening characteristics after nitriding can be obtained. If this steel pipe is used and subjected to nitriding treatment, wear resistance,
Parts with excellent seizure resistance and fatigue characteristics can be manufactured from steel pipes.

Claims (2)

[Claims] C: 0.0002 to 0.20% by weight, Si: 0.002 to 1.0%, Mn: 0.02 to 3.0%, P: 0.001 to 0.030%, S: 0.001 to 0.050%, N: 0.0002 to 0.0100. %, Balance: Fe and unavoidable impurities, and in addition to this, as a group for promoting nitriding, Al: 0.100 to 2.0%, Cr: 0.05 to 5.0%, V: 0.010 to 1.0%, Ti: 0.005 to 1.0% %, Characterized by forming a hard nitride layer on the surface of a formed body by processing and forming a steel pipe containing one or more kinds of steel pipes having excellent wear resistance and workability. 2. C: 0.0002 to 0.20% by weight, Si: 0.002 to 1.0%, Mn: 0.02 to 3.0%, P: 0.001 to 0.030%, S: 0.001 to 0.050%, N: 0.0002 to 0.0100. %, And one or more of Nb: 0.005 to 0.080%, Mo: 0.05 to 0.5%, B: 0.0003 to 0.0050%, as a selective additive element group, and the balance: Fe And inevitable impurities, and in addition, one or more of the following elements as a group for promoting nitriding: Al: 0.100 to 2.0%, Cr: 0.05 to 5.0%, V: 0.010 to 1.0%, Ti: 0.005 to 1.0%. A steel pipe excellent in abrasion resistance and workability, characterized in that a steel pipe containing two or more kinds is processed and formed, and a hard nitride layer is formed on the surface of the processed body.