Ultrahigh-strength spring steel

Patent metadata

Field	Value
Publication number	US-10487381-B2
Application number	US-201615350255-A
Country	US
Kind code	B2
Filing date	Nov 14, 2016
Priority date	Jun 21, 2016
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

An ultrahigh-strength spring steel, used as steel for a vehicle engine valve spring may include 0.5 to 0.7 wt % of C, 1.3 to 2.5 wt % of Si, 0.6 to 1.2 wt % of Mn, 0.6 to 1.5 wt % of Cr, 0.01 to 0.5 wt % of Mo, 0.01 to 0.9 wt % of Ni, 0.5 wt % or less (excluding 0 wt %) of V, 0.5 wt % or less (excluding 0 wt %) of Nb, 0.3 wt % or less (excluding 0 wt %) of Ti, 1.0 wt % or less (excluding 0 wt %) of Co, 0.1 wt % or less (excluding 0 wt %) of B, 0.3 wt % or less (excluding 0 wt %) of W, 0.3 wt % or less (excluding 0 wt %) of Cu, 0.3 wt % or less (excluding 0 wt %) of Al, 0.03 wt % or less (excluding 0 wt %) of N, 0.003 wt % or less (excluding 0 wt %) of O, and a remainder of Iron (Fe) and inevitable impurities.

First claim

What is claimed is:

1. An ultrahigh-strength spring steel, suitable for use as steel for an engine valve spring of a vehicle, the ultrahigh-strength steel consisting of: 0.5 to 0.7 wt % of Carbon (C), 1.3 to 2.5 wt % of Silicon (Si), 0.6 to 1.2 wt % of Manganese (Mn), 0.6 to 1.5 wt % of Chromium (Cr), 0.01 to 0.5 wt % of Molybdenum (Mo), 0.01 to 0.9 wt % of Nickel (Ni), 0.5 wt % or less excluding 0 wt % of Vanadium (V), 0.5 wt % or less excluding 0 wt % of Niobium (Nb), 0.3 wt % or less excluding 0 wt % of Titanium (Ti), 1.0 wt % or less excluding 0 wt % of Cobalt (Co), 0.1 wt % or less excluding 0 wt % of Boron (B), 0.3 wt % or less excluding 0 wt % of Tungsten (W), 0.3 wt % or less excluding 0 wt % of Copper (Cu), 0.3 wt % or less excluding 0 wt % of Aluminum (Al), 0.03 wt % or less excluding 0 wt % of Nitrogen (N), 0.003 wt % or less excluding 0 wt % of Oxygen (O), and a remainder of Iron (Fe) and inevitable impurities, and wherein the spring steel has a tensile strength of 3000 MPa or more, and wherein the spring steel has a hardness of 780 HV or more.

2. The ultrahigh-strength spring steel of claim 1 , wherein the spring steel has a fatigue strength of 1200 MPa or more.

3. The ultrahigh-strength spring steel of claim 1 , wherein the spring steel has a yield strength of 2500 MPa or more.

4. The ultrahigh-strength spring steel of claim 1 , wherein the spring steel endures a bending fatigue test at least 500 thousand times.

5. The ultrahigh-strength spring steel of claim 1 , wherein the spring steel has inclusions having a size of 15 μm or less.

6. The ultrahigh-strength spring steel of claim 5 , wherein the inclusions are configured such that a proportion of an inclusion having a size of 10 to 15 μm is 10% or less and a proportion of an inclusion having a size of less than 10 μm is 90% or more.

Assignees

• Hyundai Motor Co Ltd

Inventors

• Cha Sung Chul
• Kang Min Woo
• Jo Hye Min
• Hong Seung Hyun

Classifications

• C22C38/48

  with niobium or tantalum · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/42

  with copper · CPC title