ALLOYED STEEL AND QUENCHED AND TEMPERED STEEL

Abstract

The invention relates to steel with a specific composition of the following elements: 0.25%≤C≤0.35%, 0.80%≤Cr≤1.50%, 0.50%≤Ni≤1.50%, 0.0010%≤B≤0.0050%, 0.010%≤Ti≤0.060%, 0.40%≤Mn≤1.00% and 0.003%≤N≤0.0150%, whereby after being subjected to a quench and tempering treatment, the characteristics required by the ISO 898-1 standard for class 10.9 and class 12.9 bolts, screws and studs are achieved, while at the same time achieving high fatigue strength values. The use of this steel allows achieving the mentioned characteristics in large-sized parts or elements (up to a diameter of 75 mm), considerably reducing the alloying costs compared with the steels used today.

Claims

1. An Alloyed steel, consisting of the following elements in percentage by weight: 0.25%≤C≤0.35% 0.80%≤Cr≤1.50% 0.50%≤Ni≤1.50% 0.0010%≤B≤0.0050% 0.010%≤Ti≤0.060% 0.40≤Mn≤1.00% 0.0030%≤N≤0.0150% and optionally at least one of the following elements in percentage by weight: Si≤0.30% P≤0.025% S≤0.025% Cu≤0.35% Al≤0.050% Ca≤0.0050% Bi≤0.10% Pb≤0.20% Te≤0.020% Se≤0.040% balanced with iron, the remaining elements being impurities resulting from the production thereof.

2. The Alloyed steel according to claim 1, wherein the following elements have the percentages by weight indicated below: 0.30%≤C≤0.35% 0.80%≤Cr≤1.30% 0.50%≤Ni≤1.10% 0.0020%≤B≤0.0050% 0.010%≤Ti≤0.040% 0.40≤Mn≤1.00% 0.0030%≤N≤0.0100%.

3. The Alloyed steel according to claim 1, wherein at least one of the following elements have the following percentages by weight: P≤0.015% S≤0.015% Cu≤0.25% Al≤0.030%.

4. A Quenched and tempered steel produced from the alloyed steel according to claim 1, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1040 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 520 MPa.

5. A Quenched and tempered steel produced from claim 1, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1240 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 610 MPa.

6. A Method for performing a quench and tempering treatment on an alloyed steel according to claim 1, the method comprising: using an austenization temperature comprising between 800° C. to 1100° C., quenching in water or oil, using a tempering temperature between 400° C. to 650° C.

7. A Method for performing a quench and tempering treatment on an alloyed steel according claim 6, the method comprising: using an austenization temperature comprising between 850° C. to 1100° C., quenching in water or oil, using a tempering temperature between 400° C. to 650° C.

8. A Fastener made with the quenched and tempered steel according to claim 4.

9. A Foundation element of the wind-driven power generators made with the quenched and tempered steel according to claim 4.

10. The alloyed steel according to claim 2, wherein at least one of the following elements have the following percentages by weight: P≤0.015% S≤0.015% Cu≤0.25% Al≤0.030%.

11. A quenched and tempered steel produced from the alloyed steel according to claim 2, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1040 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 520 MPa.

12. A quenched and tempered steel produced from the alloyed steel according to claim 3, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1040 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 520 MPa.

13. A quenched and tempered steel produced from claim 2, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1240 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 610 MPa.

14. A quenched and tempered steel produced from claim 3, wherein the quenched and tempered steel has a mechanical strength equal to or greater than 1240 MPa, a toughness at −40° C. equal to or greater than 27 J and a fatigue strength equal to or greater than 610 MPa.

15. A method for performing a quench and tempering treatment on an alloyed steel according to claim 2, the method comprising: using an austenization temperature comprising between 800° C. to 1100° C., quenching in water or oil, using a tempering temperature between 400° C. to 650° C.

16. A method for performing a quench and tempering treatment on an alloyed steel according to claim 3, the method comprising: using an austenization temperature comprising between 800° C. to 1100° C., quenching in water or oil, using a tempering temperature between 400° C. to 650° C.

17. A fastener made with the quenched and tempered steel according to claim 5.

18. A foundation element of the wind-driven power generators made with the quenched and tempered steel according to claim 5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] To better understand the description, a set of drawings is attached in which a practical embodiment has been schematically depicted solely by way of non-limiting example.

[0082] FIG. 1 shows the diagram of the Jominy hardenability curves obtained for each of the steels presented in

[0083] Table 2, where: steel 32CrB4 is represented by a line drawn with a dash, circle and dot; 33MnBCr6 is represented by a line drawn with a dash, “x” and dot; 42CrNiMo6 is represented by a line drawn with a dot, square and dot; 34CrNiMo6 is represented by a line drawn with a dash, square and dash; and 32CrNiB4 is represented by a line drawn with a dash, triangle and dash.

Embodiments of the Invention

[0084] The comparison made between the results obtained with the steels normally used in the referred application and those obtained with the steel of the invention (32CrNiB4) is described below by way of example.

[0085] Table 2 shows the chemical compositions of the steels considered:

TABLE-US-00002 TABLE 2 Chemical composition (% by weight, except B and N in ppm) of the steels considered. Steel Steel s/EN C Mn P S Cr Ni Mo Ti B N 32CrB4 10263-4 0.32 0.81 0.012 0.012 1.13 0.00 0.00 0.030 35 72 33MnBCr6 10083-3 0.33 1.42 0.010 0.010 0.43 0.00 0.00 0.033 33 68 42CrMo4 10083-1 0.42 0.75 0.013 0.009 1.07 0.00 0.21 0.000 0 65 34CrNiMo6 10083-1 0.34 0.67 0.009 0.012 1.55 1.52 0.19 0.000 0 70 32CrNiB4 Invention 0.32 0.80 0.015 0.011 1.11 0.80 0.00 0.031 32 67

[0086] FIG. 1 shows the diagram of the Jominy hardenability curves obtained for each of the steels presented in Table 2. The steel of the invention has a curve similar to that of 34CrNiMo6 and 42CrMo4, where said curve is flat up to 20 mm of the surface; after that point there is a slight drop in hardness observed. In the case of the less alloyed steels, 32CrB4 and 33MnBCr6, the decrease in hardness is very pronounced after a distance from the quenched end of 15 mm.

[0087] All the steels referred to in Table 2 were subjected to a quench and tempering treatment. In all cases, the heat treatment conditions were optimized for each steel for the purpose of attaining the characteristics of both class 10.9 and class 12.9 bolts, screws and studs. These heat treatments were performed on bars 75 mm in diameter.

[0088] The best results obtained for each steel after the optimized quench and tempering treatment for which the characteristics of class 10.9 bolts, screws and studs are complied with are shown in Table 3.

TABLE-US-00003 TABLE 3 Results obtained for the class 10.9 bolts, screws and studs. Steel s/EN Strength KV at Fatigue limit standard (MPa) −40° C. (J) (MPa) 32CrB4 10263-4 1072 25 — 33MnBCr6 10083-3 1068 23 — 42CrMo4 10083-1 1083 69 520 34CrNiMo6 10083-1 1090 78 550 32CrNiB4 Invention 1095 74 550

[0089] Similarly, the best results attained after the quench and tempering treatment for attaining the properties of class 12.9 bolts, screws and studs in bars 75 mm in diameter are shown in Table 4.

TABLE-US-00004 TABLE 4 Results obtained for class 12.9 bolts, screws and studs. Steel s/EN Strength KV at Fatigue limit standard (MPa) −40° C. (J) (MPa) 32CrB4 10263-4 1228 17 — 33MnBCr6 10083-3 1230 15 — 42CrMo4 10083-1 1249 39 590 34CrNiMo6 10083-1 1244 56 620 32CrNiB4 Invention 1250 52 620

[0090] In the case of the two less alloyed steels, 32CrB4 and 33MnBCr6, the minimum mechanical properties required by the ISO 898-1 standard relating to bolts, screws and studs for class 10.9 and class 12.9 bolts, screws and studs are not attained in bars 75 mm in diameter.

[0091] The other three steels that were studied did meet said requirements. It can be seen how the steel of the invention allows attaining strength and low-temperature toughness values similar to those of the other two steels. Furthermore, this steel has a fatigue behavior similar to that of 34CrNiMo6 and better than that of 42CrMo4, despite having a lower alloy content.

[0092] The invention has been described according to several preferred embodiments thereof, but for the person skilled in the art it will be evident that a number of variations can be introduced in said preferred embodiments without exceeding the subject-matter of the invention that is claimed.