JPH0121846B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention is a highly hard and wear-resistant material that is used for bucket carts for civil engineering and mining machinery, loading platforms for large dump trucks, earth removal plates for bulldozers, etc. where abrasion caused by ore and earth and sand is a problem. It concerns steel plates. In general, the parts of steel used in civil engineering and mining machinery that come into direct contact with ore and earth and sand are subject to much more wear than expected, and it is said that wear determines the service life of the steel. By the way, it is known that the wear of steel materials due to ores and earth and sand is controlled by the hardness of the surface of the steel material, and the harder the steel material, the smaller the amount of wear. Figure 1 is a diagram showing the relationship between the surface hardness of steel and the amount of wear on the steel due to crushed stone, silica sand, and sand, and the amount of wear is expressed as a ratio to mild steel (SM41 material). It can also be seen from FIG. 1 that the amount of wear decreases as the surface hardness of the steel material increases. In this way, increasing the hardness of steel has been an effective means of reducing the amount of wear on steel, but increasing the hardness of steel also increases the susceptibility to delayed fracture caused by hydrogen. A difficult problem has arisen in that civil engineering and mining machines are more likely to break during production or use. and,
It has been clarified that the delayed fracture phenomenon occurs due to the hardening of the heat-affected zone that occurs when thick steel plates are cut by gas welding. It was virtually impossible to use a steel plate with good wear resistance and high surface hardness. For this reason, only steel plates with low surface hardness can be applied to civil engineering and mining machinery that has no choice but to use relatively inexpensive thick steel plates as materials, and the service life of civil engineering and mining machinery is inevitably limited by wear. The current situation was that they were forced to suffer huge economic losses. From the above-mentioned viewpoints, the present inventors have realized a high-hardness steel with good wear resistance, a surface Brinell hardness of about 360 to 600, and low susceptibility to delayed fracture, and have developed a steel material that has good wear resistance and low delayed fracture susceptibility. As a result of research aimed at improving mining efficiency and reducing operating costs, the above results were obtained.
The findings shown in (a) to (d) were obtained. That is, (a) In steel with a composition that achieves the steel hardness required for civil engineering and mining machinery, the Mn content should be 0.6 to 1.2% of that of ordinary steel (hereinafter, % indicating the composition ratio is weight %). ) to around 0.30%, the delayed fracture time will be significantly extended, and the delayed fracture resistance will be greatly improved. Figure 2 is a graph showing the correspondence between steel material hardness and delayed fracture occurrence time in a delayed fracture acceleration test in 55°C hot water, where the Mn content is 0.9 in the case where no delayed fracture resistance measures are taken. %, there is a certain correlation between the delayed fracture occurrence time and hardness of the steel material, and it is clear that the delayed fracture occurrence time becomes shorter as the hardness increases. From Figure 2, we can see that the steel material
It is also clear that when the Mn content is reduced to less than about 0.30%, the delayed fracture occurrence time is significantly extended, and the delayed fracture resistance performance is improved. Also, from Figure 2, the correspondence between the delayed fracture occurrence time and hardness of steel is unique, and if the hardness is the same, it is the same whether it is quenched and tempered or as-quenched. In particular, it is clear that it indicates the delayed failure occurrence time of
By adjusting the Mn content to a low level, even steel materials with relatively low chemical composition, such as low C materials with good weldability, can be made into materials as quenched, which is more advantageous than quenched and tempered materials. It can be seen that it is possible to achieve high hardness with good wear resistance, and to make a steel material that can sufficiently cope with delayed fracture. (b) The delayed fracture occurrence time of steel containing Sb and Pb is shorter than that of normal steel, and even if these elements are impurities, they must be reduced as much as possible from the perspective of delayed fracture. (c) Therefore, if the Mn content is sufficiently reduced and the Sb and Pb contents are reduced as much as possible by quenching, the hardness can meet the wear resistance required for civil engineering and mining machinery. It is possible to realize a steel material with excellent delayed fracture resistance. (d) Furthermore, when the hardened material is subjected to a prescribed tempering process, residual stress is reduced and leveler work for ensuring flatness becomes extremely easy. This invention was made based on the above findings, and includes: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.05 to less than 0.30%, Cr: 0.05 to 1.00%, Mo: 0.03 to 0.85. %, sol.Al: 0.010 to 0.150%, B: 0.0003 to 0.0025%, and further contains Cu: 0.05 to 0.75%, Ni: 0.05 to 1.50%, V: 0.005 to 0.250%, Nb: 0.005 ~0.150%, Ti: 0.005~0.250%, Ca: 0.0005~0.0080%, and also contains one or more of the following: Fe and unavoidable impurities: the remainder, and N, P, S, Pb and N in the impurities.
Steel with an Sb content of N: 0.0015 to 0.0100%, P: 0.018% or less, S: 0.008% or less, Pb: 0.015% or less, Sb: 0.015% or less, respectively, is heated at a temperature of 1000 to 1200°C. Hot rolling at 300°F and then quenching at a temperature above the Ac ₃ transformation point, or further at 300 to 500°C if necessary.
It is characterized in that a wear-resistant steel plate with excellent delayed fracture resistance can be obtained by tempering the steel plate. Next, in the method of the present invention, the reason why the composition ratio of the steel and the rolling/heat treatment conditions are numerically limited as described above will be explained. A. Composition of steel C. C component has the effect of improving the hardness of the steel plate, and in order to ensure a surface Brinell hardness of 360 or higher, it is necessary to add 0.15% or more, but it is necessary to add more than 0.45%. However, since the retained austenite remains untransformed, further improvement in hardness cannot be expected.
It was set at 0.15-0.45%. Si The Si component improves hardenability and temper softening resistance by adding 0.05% or more, but
If the Si content exceeds 1.00%, the toughness will deteriorate significantly, so the Si content should be reduced to 0.05% or more.
It was set at 1.00%. Mn Mn has a great effect on the delayed fracture resistance of steel, and adjusting the Mn content is the gist of the present invention. The Mn content must be at least 0.05% in order to "harden" the steel material to the center of its thickness, but among the Mn steels with a lower Mn content of around 0.3% as shown in Figure 2, Considering that Mn is unevenly distributed on the good side, the amount of Mn was strictly limited, and the Mn content was determined to be less than 0.05% to 0.30%. Note that Mn is an inexpensive element that is effective in improving the hardenability of steel, so it is added to ordinary steel in an amount of 0.6% or more, but in the method of the present invention, By keeping the Mn content low in this way, delayed fracture resistance can be dramatically improved. When reducing the Mn content of Cr steel, the hardenability decreases, but in order to compensate for the lack of hardenability,
It is necessary to contain 0.05% or more of Cr component. However, if the content exceeds 1.00%,
Since the toughness and weldability of the steel would deteriorate, the Cr content was set at 0.05 to 1.00%. Mo The Mo component coexists with B and has the effect of significantly increasing the hardenability of steel, and in order to reliably harden the steel to the center of the thickness, it is necessary to
It is necessary to contain. On the other hand, there is no need for the Mo content to exceed 0.85% in the normally used plate thickness range, and the Mo content was determined to be 0.03 to 0.85%, taking weldability into consideration. Sol.Al It is necessary to add 0.010% or more of sol.Al to improve the toughness of steel by deoxidizing it and making it grain finer, but if it is added in excess of 0.150%, the grains will become coarser. Since it causes toughness deterioration, the sol.Al content was set at 0.010 to 0.150%. B Component B is added in order to ensure the desired hardenability because it greatly improves the hardenability of steel when added in a trace amount of 0.0003% or more. However, if it is added in excess of 0.0025%, boron is formed during hardening. The B content is set to 0.0003 because it precipitates the composition and reduces the hardenability.
It was set at ~0.0025%. Cu and Ni Both of these components have the effect of improving the hardenability of steel, and are effective elements for ensuring hardening to the center of the steel plate even when the thickness of the steel plate increases. Therefore, they can be added as necessary, but when direct hardening is performed, the hardenability is improved compared to reheat hardening, so the amount of alloying elements of Cu and Ni added as the plate thickness increases. less is better. The reasons for limiting the content by numerical value for each will be explained in detail below. (i) Cu Cu component can improve the hardenability of steel by adding 0.05% or more, but 0.75% or more
Since no further improvement effect can be obtained even if the Cu content is added in excess of 0.05~
It was set at 0.75%. In addition, when directly quenching, a sufficient effect can be obtained with a content of 0.50% or less. (ii) Ni Ni is also an element that increases the hardenability of steel when added in an amount of 0.05% or more, and it does not deteriorate toughness, so it is extremely effective for improving hardenability. Since Ni is an expensive element, the Ni content was set at 0.05 to 1.50% in consideration of economic efficiency. In addition, when directly quenching, a sufficient effect can be obtained with a content of 1.00% or less. ○…

Claims (1)

[Claims] 1. In weight percentage: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.05 to less than 0.30%, Cr: 0.05 to 1.00%, Mo: 0.03 to 0.85%, sol.Al : 0.010 to 0.150%, B: 0.0003 to 0.0025%, and further contains Cu: 0.05 to 0.75%, Ni: 0.05 to 1.50%, V: 0.005 to 0.250%, Nb: 0.005 to 0.150%, Ti: 0.005 ~0.250%, Ca: 0.0005~0.0080%, and also contains Fe and inevitable impurities: the remainder, and N, P, S, Pb and
Steel with an Sb content of N: 0.0015 to 0.0100%, P: 0.018% or less, S: 0.008% or less, Pb: 0.015% or less, Sb: 0.015% or less, respectively, is heated at a temperature of 1000 to 1200°C. 1. A method for producing a wear-resistant steel sheet with excellent delayed fracture resistance, the method comprising hot rolling at a temperature of at least 100 nm, followed by quenching at a temperature equal to or higher than the Ac ₃ transformation point. 2. The method for producing a wear-resistant steel sheet with excellent delayed fracture resistance according to claim 1, wherein the quenching treatment is direct quenching performed without lowering the temperature below the Ar ₃ transformation point after rolling. 3 In terms of weight percentage, C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.05 to less than 0.30%, Cr: 0.05 to 1.00%, Mo: 0.03 to 0.85%, sol.Al: 0.010 to 0.150%, Contains B: 0.0003-0.0025%, Cu: 0.05-0.75%, Ni: 0.05-1.50%, V: 0.005-0.250%, Nb: 0.005-0.150%, Ti: 0.005-0.250%, Ca: 0.0005 to 0.0080%, and also contains one or more of the following: Fe and unavoidable impurities: the remainder, and N, P, S, Pb and
Steel with an Sb content of N: 0.0015 to 0.0100%, P: 0.018% or less, S: 0.008% or less, Pb: 0.015% or less, Sb: 0.015% or less, respectively, is heated at a temperature of 1000 to 1200°C. Production of a wear-resistant steel sheet with excellent delayed fracture resistance, characterized by hot rolling at a temperature of 300°C, followed by quenching at a temperature above the Ac ₃ transformation point, and then tempering at 300 to 500°C. Method. 4. The method for producing a wear-resistant steel sheet with excellent delayed fracture resistance according to claim 2, wherein the quenching treatment is direct quenching performed without lowering the temperature below the Ar ₃ transformation point after rolling.